Decision-Making and Management of Immature Permanent Teeth with Crown Fractures in Small Animals—A Review

Introduction

Tooth fractures are a known cause of endodontic compromise in small animals.^1,2 A visual survey of 63 anesthetized dogs presented for problems other than oral disease at a veterinary teaching hospital found that 27% had fractured teeth, and 10% had fractured teeth with pulp exposure. ³ Crown fractures have been found to affect 29% of dogs and cats with other maxillofacial trauma, ⁴ and young dogs and cats are more prone to dental injuries than older animals with similar trauma. ⁴ Similar findings have been reported in humans,^5,6 with most traumatic dental injuries occurring in humans before age 19. ⁷ Crown fractures are one of the most commonly occurring dental injuries in animals and humans.^4,7 Failure to treat endodontically compromised immature permanent teeth risks the premature loss of the functioning pulp, and a lifetime of poor structure and function for affected teeth.^7,8 Loss of pulp function during early tooth development results in thin and fragile dentin walls, incomplete formation of root apices, and increased crown-to-root ratio.^8–10 It is therefore important to recognize and treat endodontically compromised teeth, particularly if the injury occurs during early tooth development. Determining the appropriate treatment depends on pulp viability, extent of alveolar bone loss, ongoing/future risk of damage, and the owner's willingness to pursue treatment.

Injuries resulting from trauma of presumably higher impact, such as vehicular accidents or being hit by an object, are more likely to cause dental injury. ⁴ Dental injuries may result in a normal pulp, reversible pulpitis, or irreversible pulpitis, with or without pulp exposure. ¹¹ Selection of the most appropriate endodontic treatment for immature permanent teeth is based on several factors, the most important of which is whether the pulp is vital or nonvital. Techniques for treating teeth that have vital pulp tissue include bonding and sealing, indirect pulp capping, and pulpotomy with direct pulp capping/vital pulp therapy. These can all lead to the physiological formation of the tooth root and apex. Techniques for treating teeth that have nonvital pulp tissue include regenerative endodontic therapy or apexification followed by conventional root canal therapy. This article reviews the indications for these techniques and condenses and consolidates treatment protocols for each.

Assessment of Tooth Injuries

Human case histories include reports of pain and patient responses to sensitivity/sensibility testing of injured teeth. These are important for the determination of pulp health status in humans.^11,12 Veterinary patients do not reliably demonstrate signs of dental pain or discomfort, and the interpretation of percussive, thermal, or electric pulp tests in dogs and cats can be challenging.^13–15 Ultimately, history, clinical examination, and radiographic assessment comprise the standard approach for assessing tooth injuries in veterinary patients.

Type of trauma can determine the likelihood of tooth injury. A recent study found that dog and cat patients who sustained maxillofacial trauma due to motor vehicle accidents or being hit by an object were 40% more likely to sustain dentoalveolar injuries when compared with those who were involved in seemingly lower impact events, such as altercations with other animals. ⁴ Timeline can be important for determining appropriate treatment options. For example, vital pulp therapy should ideally be performed as soon as possible after injury, although specific guidelines vary. Pulp inflammation can progress to an irreversible state over time, so prompt treatment is recommended. A complete history including current medications may be important. Although not prescribed commonly to young patients, some immunosuppressive medications such as cyclosporine can impede repair after endodontic treatment in dogs. ¹⁶ In one study, dogs treated with cyclosporine or other immunosuppressive drugs were found to develop more inflammation and pulp necrosis after vital pulp therapy and exhibit less repair. ¹⁶ The precise mechanism is not known but may be due to disruption of repair through inhibition of cytokine release. ¹⁶ On the other hand, prednisone (dosed at 1 mg/kg/day) did not appear to inhibit repair and showed the same successful results as the control group. ¹⁶

After a traumatic episode, it is important to establish that the patient is stable and in good overall health before performing further diagnostics for fractured teeth. During the awake examination, the patient can be evaluated for fractured or discolored teeth, facial symmetry, and occlusal abnormalities. With the patient under anesthesia, a complete oral examination is performed, starting with a visual inspection for draining sinus tracts and swelling, then use of a dental explorer and probe to assess pulpal exposure and periodontal lesions.

Dental radiographs are important for assessing tooth development and endodontic health. At the time of eruption of the permanent tooth, only about 50% of the expected tooth root length has formed. ¹⁷ Depending on the tooth, the root apices have been found to close in dogs between 7 and 10 months of age.^18,19 In cats, root apices have been found to close between 7 and 11 months of age. ²⁰ Therefore, until small animals are 10-11 months of age, their apices may be open. This is important because treatment recommendations depend on the status of apical closure. Also, even if the apex has closed, the dentin remains thin in young animals, resulting in recommendations to maintain pulp vitality in patients 18 months or younger. ²¹ Thin dentin predisposes the tooth to fracture, ²² a possible explanation for the higher incidence of tooth injury found in young animals and children with facial injuries.^4,6 Behavioral patterns in young animals and children may also predispose them to more facial and dental injuries. ⁴

A critical factor in decision-making for the treatment of endodontically compromised teeth is whether the pulp is vital or nonvital. Lack of bleeding during probing/exploration, presence of a draining tract, and/or foul odor are signs of necrotic pulp tissue. Intrinsic staining/discoloration or vestibule swelling may also be seen in nonvital teeth. ²³ An important 2001 retrospective study in dogs found, on visual examination, signs of partial or total pulp necrosis in 92.2% of teeth with intact but entirely discolored crowns. ¹⁵ Fractured teeth have experienced trauma and may become discolored. Radiographically, any evidence of periapical lucency indicates that the pulp is nonvital, ²³ along with other possible radiographic changes. ¹⁵ For example, arrested tooth maturation,^15,24 including thinner dentin walls, shorter root length, and less apical development in comparison with the contralateral tooth, are also indicators of nonvital pulp.

After crown fractures, the pulp may be normal, inflamed, or nonvital/necrotic. ¹¹ A normal pulp may be present only if the fracture is uncomplicated and the trauma has not caused pulpal inflammation (pulpitis). In complicated crown fractures, pulpitis invariably occurs. The question is whether the pulpitis is reversible or irreversible. Reversible pulpitis is defined as “a clinical diagnosis based on subjective and objective findings indicating that the inflammation should resolve and the pulp return to normal.” ²⁵ Irreversible pulpitis is defined as “a clinical diagnosis based on subjective and objective findings indicating that the vital inflamed pulp is incapable of healing.” ²⁵ Subjective findings allowing a diagnosis of reversible versus irreversible pulpitis, such as response to noxious stimuli, can be difficult to determine in children ²⁶ and animals.^14,15 Sometimes this necessitates treatment decisions based on intraoperative findings.^8,26 Some objective determinants of irreversible pulpitis include “excessive or deep purple hemorrhage from an exposed or amputated pulp,” ⁸ or persistent hemorrhage for greater than 5 min following partial coronal pulpotomy. ²⁷ In treating immature permanent teeth, recommendations often indicate starting with the least invasive treatment options available, then progressing to more invasive techniques as needed. The ultimate goal in treating endodontically compromised immature permanent teeth is to preserve pulp vitality and allow continued dental development.^21,26

Treatment options for endodontically compromised, immature, traumatized teeth that have vital pulps include (1) odontoplasty, bonding, and sealing ± restoration; (2) indirect pulp capping; and (3) vital pulp therapy. Treatment options for immature teeth that have nonvital pulps include (1) apexification with root canal therapy; and (2) regenerative endodontics. Decisions are based on a systematic evaluation of the affected tooth. In cases with an infection that cannot be controlled, extensive alveolar bone loss that cannot be reversed, ongoing/future risk of damage, extensive root resorption, insufficient crown structure remaining for restoration, or in cases where owners are unwilling/unable to pursue treatment that may require ongoing monitoring, exodontia is considered to be an alternative treatment option.^9,12 A decision-making algorithm for the management of immature permanent teeth with crown fractures is provided to assist in treatment planning (Figure 1).

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Figure 1.

Decision-making algorithm for the management of immature permanent teeth with crown fractures.

Uncomplicated Crown Fractures—Odontoplasty with Bonding and Sealing ± Restoration or Indirect Pulp Capping

In humans, uncomplicated crown fractures are likely the most common type of dental trauma and comprise at least one-third to one-half of all reported dental trauma.^28,29 A recent veterinary study reporting on traumatic dentoalveolar injuries in dogs and cats found the frequency of uncomplicated crown fractures to be 16.2%. ³⁰ Uncomplicated crown fractures can have a significant dentin barrier remaining or can have a thin layer of dentin over the pulp. In the human and veterinary literature, a tooth fracture is considered to have caused “near pulp exposure” when the remaining dentin thickness overlying the pulp is approximately 0.5 mm or less.^10,21,28 Other veterinary references consider near pulp exposure to be at a dentin thickness of less than 1-2 mm.^21,31 When the fracture is very close to the pulp, a pinkish hue is visible when approximately 0.5 mm of dentin remains. ¹⁰ The closer the fracture is to the pulp, the more sensitive or painful the tooth will be. ¹⁰ In dogs, dentin has been found to be nearly twice as porous as in humans, ³² which may account for the difference in definition of “near pulp exposure” between references. If the uncomplicated crown fracture does not have near pulp exposure—that is, is superficial—then an odontoplasty is performed, and restorative materials of choice can be used to repair and protect the tooth. ³² In humans, with modern bonding options, the tooth fragment may be reattached for the best possible aesthetic result. ²³ This has not yet become the standard of care in animals, but may be forthcoming, depending on patient temperament. If the uncomplicated crown fracture does have near pulp exposure, then the pulp can have a negative reaction to the etching and bonding process, and a protective layer of hard-setting calcium hydroxide or other base layer material should be applied prior to restoration.^21,28 The veterinary literature often refers to this minimally invasive treatment of fractured teeth as indirect pulp capping,^21,33,34 while the human literature reserves this term for the treatment of deep dental caries. ²⁵ In many cases, indirect pulp capping (veterinary use) may not be possible due to poor potential for restoration retention. ³³ In those cases, vital pulp therapy may be a better treatment option, because a well-placed restoration without microleakage may be more important than the pulp cap itself for maintaining pulp vitality.^28,35 In addition, a simple odontoplasty procedure, through aggressive dentin removal, may result in near pulp exposure or pulp exposure, necessitating conversion to an indirect or direct pulp capping procedure.^11,36 The operator should prepare for all eventualities.

For superficial crown fractures treated by odontoplasty, bonding, and sealing, recall recommendations vary, including at least clinical and radiographic follow-up 6-12 months postoperatively,^32,37 with possible ongoing monitoring every 6-12 months thereafter. ³⁸ For uncomplicated crown fractures with near pulp exposure (treated with indirect pulp capping), the recall recommendations are less well-documented but could benefit from recall intervals similar to those recommended for direct pulp capping, with more prolonged ongoing monitoring, due to the possibility of later treatment failure.^14,39 Acute or chronic dental trauma, even without pulp exposure, may result in eventual pulp necrosis, ¹³ which will not be immediately apparent.

The steps in the treatment of vital teeth that have uncomplicated crown fractures without near pulp exposure have been previously described^{31,32,34,37,38} and are outlined in Table 1. The steps in the treatment of vital teeth that have uncomplicated crown fractures with near pulp exposure have also been previously described^8,21,34,39 and are outlined in Table 2.

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Table 1.

Vital Tooth with Uncomplicated Crown Fracture Without Near Pulp Exposure: Protocol for Odontoplasty and Bonding +/− Composite Restoration.^{31,32,34,37,38}

Step 1	Radiograph the tooth for baseline status. Do not use this treatment if there are any signs of nonvitality.
Step 2	Ultrasonically scale the tooth. Polish with fluoride-free pumice.
Step 3	Odontoplasty—smooth the fractured dentin and enamel using a conical white stone or fine diamond bur on a high-speed handpiece, followed by polishing discs (progressing from coarser to finer). Rinse between each smoothing step to remove debris.
Step 4	Apply acid etch gel to the fracture site, slightly overlapping the adjacent enamel, for 30 s (or according to manufacturer's recommendations). Rinse for 30 s, gently dry using clean, oil-free air. Do not desiccate.
Step 5	Apply a thin layer of bonding agent to the prepared site with a microbrush, air-thin, and light cure per manufacturer's instructions.
Step 6	Optional step: Depending on defect size and potential for retention of a composite restoration, composite material is placed over the bonding agent, shaped, and light-cured per manufacturer's instructions. Polish for a smooth, finished surface.
Step 7	Apply a thin layer of unfilled resin with a microbrush, air-thin, and light cure per manufacturer's instructions.
Step 8	The tooth should be reevaluated and radiographed 6-12 months following treatment to monitor for signs of endodontic disease. Ongoing monitoring with radiographs is recommended periodically.

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Table 2.

Vital Tooth with Uncomplicated Crown Fracture with Near Pulp Exposure: Protocol for Indirect Pulp Cap.^8,21,34,39

Step 1	Radiograph the tooth for baseline status. Do not use this treatment if there are any signs of nonvitality.
Step 2	Ultrasonically scale the tooth. Polish with fluoride-free pumice.
Step 3	The pink hue of the pulp is often seen through the dentin in teeth with near pulp exposure. Care should be taken not to penetrate the pulp during odontoplasty. Smooth the fractured dentin and enamel using a conical white stone or fine diamond bur on a high-speed handpiece, followed by polishing discs (progressing from coarser to finer). Rinse between each smoothing step to remove debris.
Step 4	The initial or base layer should be placed to ensure complete coverage of the clean, dry dentin overlying the near pulp exposure, but avoiding contact with the more peripheral dentin surrounding the near pulp exposure. Current studies primarily recommend hard-setting calcium hydroxide, MTA, or newer generation bioceramic materials as the base layer. The base layer should be cured according to manufacturer's recommendations.
Step 5	The base layer may be followed for added sealing and immediate stability by the application of a glass ionomer or resin-modified glass ionomer (GI or RMGI). This can also reduce the depth and therefore shrinkage of the composite restoration. Avoid contact with the periphery in the area of the final restoration. Cure according to manufacturer's recommendations.
Step 6	Apply acid etch gel to the prepared site, slightly overlapping the adjacent enamel, for 30 s (or according to manufacturer's recommendations). Rinse for 30 s, gently dry using clean, oil-free air. Do not desiccate.
Step 7	Apply a thin layer of bonding agent to the prepared site with a microbrush, air-thin, and light cure per manufacturer's instructions.
Step 8	Place the composite restoration over the bonding agent, shaping and light-curing it per manufacturer's instructions. Polish for a smoother, finished surface.
Step 9	Place a final thin layer of unfilled resin using a microbrush, with light curing per manufacturer's instructions.
Step 10	The tooth should be reevaluated and radiographed 6-12 months following treatment to monitor for signs of endodontic disease. Ongoing annual monitoring is recommended for at least 5-6 years if adhering to similar guidelines for direct pulp capping.

Note. MTA, mineral trioxide aggregate.

Complicated Crown Fractures in Vital Teeth—Partial Pulpotomy with Direct Pulp Cap/Vital Pulp Therapy

Complicated crown fractures are estimated to occur in up to 13% of all human dental injuries. ²⁸ In dogs and cats, complicated crown fractures were found to comprise 49.6% of all dentoalveolar injuries in a recent veterinary study. ³⁰ Maintaining pulp vitality is especially important for immature teeth so they can continue to develop.^8,14,40 For immature teeth with complicated crown fractures and vital pulps, the treatment of choice is direct pulp cap/vital pulp therapy. Published timing for vital pulp therapy treatment following pulp exposure has varied widely, from a few hours to 3 weeks.^{17,21,27,33,41} Older retrospective veterinary studies from 2001 found greater success when vital pulp therapy was performed sooner after pulp exposure.^27,41 However, a 2014 review of 190 vital pulp therapies in dogs found no significant correlation between time of pulp exposure to treatment and success of treatment, ³³ with time since exposure ranging from 3 to 250 h (median 24 h). For immature teeth, the human literature states, “Neither time between the accident and treatment nor size of exposure is critical if the inflamed superficial pulp tissue is amputated to healthy pulp.” ¹² Nonetheless, unnecessary delays and indifference to the problem should be avoided. ⁴² Delaying treatment can only lead to additional problems, such as infection, pain, and tooth loss. ⁴² Ideally, if a tooth with traumatic pulp exposure is to be treated with vital pulp therapy, it should be treated as soon as possible. Time constraints imposed by life-threatening injuries, impaired access to advanced dental care, and/or failure to recognize fractured teeth and the need for care ¹³ may unavoidably delay treatment.

Due to limited treatment options for fractured, immature vital teeth with open apices and/or thin dentin walls, vital pulp therapy should be attempted if there is a chance of debriding down to vital pulp tissue. ¹² Vital pulp therapy affords the tooth the opportunity to continue to develop, even if it becomes nonvital at a later date, requiring conventional endodontic therapy.^41,43,44 Ongoing follow-up is recommended. Given that pet owner observations are not reliable in determining the success of vital pulp therapy, radiographic monitoring is required^14,41 for adequate assessment. Standard human recall intervals, including clinical and radiographic evaluations, are recommended approximately 6-12 weeks, then 6 and 12 months after treatment, then annually for 5 years, or up to 10 years. ⁴⁵ Recent veterinary sources^14,33 derive their recommendations from the human literature. The slightly modified veterinary recommendations include radiographic follow-up 3-6 months posttreatment, then 12 months posttreatment, then annually. ³³ Because failure of vital pulp therapy may occur years later, these teeth should be monitored for at least 5 or 6 years after treatment. ¹⁴ Clinical monitoring includes assessment for signs of pulp necrosis, such as draining tracts, ¹³ swelling, pain, and intrinsic color change of the crown.^23,45 Even if white mineral trioxide aggregate (MTA) is used for vital pulp therapy, there remains a possibility of coronal discoloration which should not be assumed to be an indicator of pulp necrosis. ¹¹ Radiographic evaluation should include signs of apical closure, continued root development, ongoing dentin formation, dentin bridge formation, periapical lucency, external and internal resorption, and changes to the restoration.^8,33 Although historically the presence of a dentin bridge has been considered to be a sign of successful vital pulp therapy, recent references indicate that the presence of a dentin bridge does not ensure success, nor does the absence of a dentin bridge signify failure.^33,46 Pulp canal calcification/obliteration may also not be considered a sign of failure. ⁸

In some cases, it may be necessary to convert a tooth with near pulp exposure to a tooth with pulp exposure. As discussed above, a poor prognosis for restoration retention in a tooth with near pulp exposure is an indication for direct pulp capping/vital pulp therapy rather than indirect pulp capping, even if intentionally exposing the pulp is required. ³³

Avoiding Failure

Deep penetration of the pulp dressing material into the pulp is associated with failure of direct pulp cap/vital pulp therapy. ³³ In a 2014 retrospective study of vital pulp therapies in dogs, deep penetration occurred more frequently when calcium hydroxide was used, possibly due to its more flowable properties as compared with MTA. ³³ The pulp chamber of immature canine teeth in dogs and cats widens acutely as it extends apically in a funnel shape. ³³ If the fracture occurred coronal to this funnel shape, then the pulp exposure site should be widened by gently removing dentin circumferentially. This allows adequate exposure of the entire surface of the proposed pulpotomy site for amputation with a diamond bur of similar width.^8,21,47 This results in the entire roof of the pulp chamber being removed. ⁸ The widened anatomy at this funnel-like site in canine teeth was thought to account for inappropriate clot formation and deep penetration of the pulp dressing material in the 2014 retrospective study of vital pulp therapies. ³³ It seems logical that, without sufficient visibility, it may be difficult to discern whether the pulp has been adequately debrided of diseased tissue, and it may be difficult to place an even layer of pulp dressing. Thus, poor access to the entire surface of the pulpotomy site through this funnel-like area may lead to (a) inadequate pulp debridement,^21,47 (b) inadequate hemorrhage control, ³³ and (c) inadequate access for proper placement of pulp dressing. Ensuring that the pulpotomy access site is adequately widened for visualization and approach to the entire debrided pulp surface may avoid these complications.

Pulp Flushing/Blotting Solutions

In most veterinary literature, sterile saline is used gently to flush or blot the debrided pulp surface.^21,33 In the human literature, various strengths of sodium hypochlorite (NaOCl) are also recommended for this purpose.^28,29,48 A cotton pellet or the blunt end of a paper point moistened with saline^21,33,47 or with NaOCl^26,48 has most often been described for hemorrhage control. A recent, major veterinary dentistry reference text has also mentioned the possibility of using a lavage of bleach for hemostasis, stating that it has no adverse effect on pulpal healing, even if refreshed and left in contact with the pulp for 10-15 min. ¹⁷ Saline induces the mildest pulp response and is used in most studies; NaOCl induces increased inflammatory response in the pulp but provides enhanced hemorrhage control. ⁴⁸ “The bleach causes chemical amputation of the blood coagulum; removes damaged pulp cells, dentin chips, and other debris; and provides hemorrhage control with minimal damage to the “normal” pulp tissue underneath.” ²⁸ NaOCl “is not only antimicrobial but appears to have no adverse effects on pulpal healing, odontoblastic cell formation, or dentinal bridging.” ⁸ A recent in vitro study examining the response of stem cells of the apical papilla to NaOCl in various concentrations found the best cell survival and differentiation in the populations irrigated with 1.5% NaOCl. ⁴⁹ Cell populations irrigated with 17% EDTA after NaOCl showed some reversal of negative effects. ⁴⁹ An in vivo report on regenerative endodontic procedures in dogs found that a 2-min final rinse with 17% EDTA after NaOCl had a positive impact on outcome. ⁵⁰ Therefore, flushing pulp or other stem cell-containing areas with 1.5% NaOCl, or 1.5% NaOCl followed by 17% EDTA may be beneficial. ⁴⁹

Calcium Hydroxide Versus MTA Versus Bioceramic Materials

Various materials have been recommended for use as pulp dressings in direct pulp capping/vital pulp therapy. A 2014 retrospective study of vital pulp therapies in dogs found that the overall failure rate for vital pulp therapy with calcium hydroxide was greater than 5 times that with mineral trioxide aggregate, or MTA. ³³ MTA, a first-generation bioceramic material, has been found to be a good pulp capping agent in humans but brings the disadvantages of potential coronal discoloration and may require a 2-step treatment in humans. ²⁸ Newer generations of bioceramic materials (including newer generations of MTA) have shown promise for use as pulp capping agents due to their faster setting times and decreased risk of tooth discoloration. ²⁸

Antibiotic Therapy

Antibiotic therapy was not found to be significantly associated with the outcome of vital pulp therapy in dogs in a 2014 retrospective study. ³³ Vital pulp therapy alone does not require the use of antimicrobials. ³³ The human literature currently recommends using antibiotics conservatively in endodontic practice. ⁵¹

The protocol for the treatment of vital teeth with complicated crown fractures using direct pulp cap/vital pulp therapy has been previously described and is outlined in Table 3.^{21,26,28,29,33,34,43,47,52}

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Table 3.

Vital Tooth with Complicated Crown Fracture: Protocol for Partial Pulpotomy with Direct Pulp Cap/Vital Pulp Therapy.^{21,26,28,29,33,34,43,47,52}

Step 1	Radiograph the tooth for baseline status. Do not use this treatment if there are any signs of loss of tooth vitality.
Step 2	Ultrasonically scale the affected tooth and polish using fluoride-free pumice. Lavage the oral cavity with a 0.12% chlorhexidine solution. 53 Isolate the affected tooth using a rubber dam. Expand the sterile working area using sterile towels or drapes.
Step 3	Remove approximately 5-7 mm of coronal pulp using an appropriately sized, sterile pear-shaped or round diamond bur (similar in width to that of the pulp at the level of pulpotomy). If deep purple hemorrhage persists or if hemorrhage cannot be controlled after 5 min, then a deeper pulpotomy is indicated to reach healthy pulp tissue. As needed, gently remove dentin circumferentially around the walls of the access site to ensure adequate exposure of the entire floor of the proposed pulpotomy.
Step 4	Gently flush the surface of the exposed pulp with sterile saline (0.9% NaCl) or with sodium hypochlorite (1.25%-6% NaOCl has been reported, although the lower concentrations are less cytotoxic). Flushing with 1.5% NaOCl followed by 17% EDTA may be most beneficial. Bleeding may be controlled with the blunt end of a paper point or cotton pellet moistened with saline or sodium hypochlorite.
Step 5	After hemostasis is achieved, a 2-3 mm layer of MTA, calcium hydroxide, or other chosen bioceramic material should be placed gently over the debrided, healthy pulp as the pulp dressing. Care should be taken not to penetrate into the pulp tissue and avoid contact of the pulp dressing with the more coronal dentin walls. If any pulp dressing has adhered to the more coronal dentin walls, it should be gently removed.
Step 6	A 1 mm layer of glass ionomer restorative is then applied over the pulp dressing material per manufacturer's instructions. Care should be taken to avoid contact of the glass ionomer with the more coronal dentin walls. 21 If any glass ionomer restorative has adhered to the coronal dentin walls, it should be gently debrided prior to preparation for the final restoration. The glass ionomer restorative is sandwiched between the pulp dressing material and the final composite restoration and helps to minimize microleakage.
Step 7	Apply acid etch gel to the prepared site, slightly overlapping the adjacent enamel, for 30 s (or according to manufacturer's recommendations). Rinse for 30 s, gently dry using clean, oil-free air. Do not desiccate.
Step 8	Apply a thin layer of bonding agent to the prepared site with a microbrush, air-thin, and light cure per manufacturer's instructions.
Step 9	Place the composite restoration over the bonding agent, shaping and light curing it per manufacturer's instructions. Polish for a smoother, finished surface.
Step 10	Place a final, thin layer of unfilled resin using a microbrush, with light curing per manufacturer's instructions.
Step 11	Clinical and radiographic follow-up for vital pulp therapies is recommended 3-6 months posttreatment, then 12 months posttreatment, then annually 33 for at least 5-6 years. 14

Note. MTA, mineral trioxide aggregate.

Complicated Crown Fractures in Nonvital Teeth—Apexification or Regenerative Endodontic Therapy

Immature, nonvital teeth present a particular treatment challenge because of their thin dentin walls, incomplete root development, and open apices. Because of these qualities, they are weaker and more at risk of fracture. In humans, it has been reported that 30% of these teeth fracture during or after endodontic treatment. ²⁸

Apexification has been defined as “a method to induce a calcified barrier in a root with an open apex or the continued apical development of an incompletely formed root in teeth with necrotic pulps.” ²⁵ Regenerative endodontics have been defined as “biologically-based procedures designed to physiologically replace damaged tooth structures, including dentin and root structures, as well as cells of the pulp-dentin complex.” ²⁵

For decades, apexification has been the primary endodontic treatment option for immature, nonvital teeth with open apices in humans, and has been described in several reports in dogs and cats.^54–57 There are numerous human patient reports of successful apexification treatment either using calcium hydroxide and multiple visits or using MTA or other bioceramic materials in 1- or 2-step procedures.^28,58–61 These techniques have been in use for years.^28,58 However, since 2001, reports of successful management of nonvital immature teeth utilizing regenerative endodontic therapy have been growing rapidly, to the point that apexification has begun to fall out of favor for human patients.^28,54,58,62

Treatment of nonvital immature teeth that have crown fractures utilizing traditional multistep apexification with calcium hydroxide has been previously described and is outlined in Table 4.^21,55,63,64

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Table 4.

Nonvital Immature Tooth with Crown Fracture: Protocol for Traditional Apexification with Calcium Hydroxide Treatment, Multistep.^21,55,63,64

Step 1	Confirm lack of tooth vitality and open apex status via clinical examination and dental radiography.
Step 2	Ultrasonically scale the affected tooth and polish using fluoride-free pumice. Lavage the oral cavity with a 0.12% chlorhexidine solution. 53 Isolate the affected tooth using a rubber dam. Expand the sterile working area using sterile towels or drapes.
Step 3	Create an endodontic access if the fracture site does not allow for adequate straight-line access to the apical region of the tooth by endodontic files. The access site must be wide enough in comparison with the canal size to allow for adequate instrumentation and filling.
Step 4	Carefully place an endodontic file to the apical limit. Determine the working length by stopping 1-2 mm short of the apex, utilizing radiographs and setting an endodontic stop at this length, avoiding trauma to the apical and periapical tissues.
Step 5	Very light filing, in a gentle circumferential motion, is performed on the innermost dentin walls using copious negative pressure irrigation and an irrigation needle with 0.5%-5.25% NaOCl. Most resources advise using lower NaOCl concentrations, 0.5%-1.5%, to reduce the risk of patient injury if the liquid passes through the apex. 28 The goal is to achieve mild debridement without disrupting the thin dentin walls. Continue to flush gently until the emerging irrigant is clear. An optional final flush with sterile saline may be performed. Flushing with 1.5% NaOCl followed by 17% EDTA may be most beneficial.
Step 6	Using gentle suction, remove any remaining excess fluid. With the blunt ends of paper points, carefully dry the canal to the level of the working length.
Step 7	Disinfection of the canal is achieved by filling the canal with calcium hydroxide paste for 1-4 weeks. Fill the canal with calcium hydroxide paste of a toothpaste-like viscosity. Either a spiral paste filler or a syringe with an appropriately sized catheter attached may be used to reach the working length of the canal, backfilling the canal while slowly withdrawing the spiral paste filler or the catheter tip. Either a commercially available calcium hydroxide paste or a hand-mixed paste of calcium hydroxide powder and sterile saline may be used.
Step 8	Radiograph the tooth to ensure complete filling of the canal to the working length. If voids are present, repeat Step 7.
Step 9	Meticulously remove the calcium hydroxide to within 3 mm apical of the access site. Place a temporary restoration (CavitTM a, IRMTM b, glass ionomer, or another temporary material) at the access site and fracture site (if there are 2 sites).
Step 10	Human endodontists recommend changing out the calcium hydroxide paste 1-4 weeks after initial placement, in exchange for a firmer calcium hydroxide plug at the apex. In veterinary medicine, traditionally the initial calcium hydroxide paste filling is left in the tooth until the hard tissue apical barrier forms. If using the human endodontic approach, recall the patient 1-4 weeks after initial calcium hydroxide placement to change out the calcium hydroxide paste for a firmer calcium hydroxide apical plug. Then, with either approach, recall the patient every 3 months for clinical examination and dental radiographs, to check for resolution of clinical signs and formation of a calcified apical barrier at the affected tooth. This process may take 3-24 months but may occur in just a few months in young veterinary patients. If the calcified apical barrier has not formed and washout of calcium hydroxide has occurred, then the calcium hydroxide should be replaced and the monitoring continued.
Step 11	When the clinical signs associated with the affected tooth have resolved, and the dental radiographs show calcified barrier formation at the apex, then the temporary restoration may be removed and the canal debrided of calcium hydroxide. This is achieved by irrigation with sterile saline or NaOCl. The working length is redetermined, and the tooth obturated and restored using conventional endodontic techniques.
Step 12	Clinical and radiographic follow-up for conventional endodontic therapy is recommended 6 and 12 months posttreatment, then annually for 5 years.21,65

Calcium hydroxide apexification techniques require multiple visits and it can take many months for the apical hard tissue barrier to form.^54,66 Long-term treatment with calcium hydroxide may also weaken the tooth roots, ²⁸ increasing the risk of fracture. ⁵⁴ Therefore, alternative techniques using MTA or other bioceramic barrier materials were developed to achieve an apical barrier more quickly and more reliably.^54,59,67 With MTA and other bioceramic materials, the apical barrier is created immediately upon placement at the apex of the immature tooth, without the need for pretreatment with calcium hydroxide.^54,67,68 The tooth can then be obturated as in standard root canal therapy. When MTA apical barrier plugs were first developed, the materials required longer curing times (3-4 h minimum), so a 2-visit procedure was often used to allow for curing, or an intermediate layer of glass ionomer was placed over the MTA plug.^29,67,69 Still, some investigations obturated the canal immediately after placement of the apical MTA plug.^59,70 Newer bioceramic materials, such as MTA Angelus^c or Biodentine,^d with faster curing times, may facilitate 1-visit apexification procedures,^26,54 and some reports promote 1-visit apexification with the original MTA formulation. ⁷⁰ Whenever MTA is used, there is a possibility for discoloration within the tooth even if the treatment is successful,^11,28 but the risk of discoloration is likely lower if the MTA is localized at the apex.

Treatment of nonvital immature teeth that have crown fractures achieving apexification using MTA or other bioceramic materials has been previously described and is outlined in Table 5.^{28,29,56,57,59,67,70}

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Table 5.

Nonvital Immature Tooth with Crown Fracture: Protocol for Apexification Using MTA or Other Bioceramic Materials.^{28,29,56,57,59,67,70}

Step 1	Confirm lack of tooth vitality and open apex status via clinical examination and dental radiography.
Step 2	Ultrasonically scale the affected tooth and polish using fluoride-free pumice. Lavage the oral cavity with a 0.12% chlorhexidine solution. 53 Isolate the affected tooth using a rubber dam. Expand the sterile working area using sterile towels or drapes.
Step 3	Create an endodontic access if the fracture site does not allow for adequate straight-line access to the apical region of the tooth by endodontic files. The access site must be wide enough in comparison with the canal size to allow for adequate instrumentation and filling.
Step 4	Carefully place an endodontic file to the apical limit. Determine the working length by stopping 1-2 mm short of the apex, utilizing radiographs and setting an endodontic stop at this length, avoiding trauma to the apical and periapical tissues.
Step 5	Very light filing, in a gentle circumferential motion, is performed on the innermost dentin walls using copious negative pressure irrigation and an irrigation needle with 0.5%-5.25% NaOCl. Most resources advise using lower NaOCl concentrations, 0.5%-1.5%, to reduce the risk of patient injury if the liquid passes through the apex. 28 The goal is to achieve mild debridement without disrupting the thin dentin walls. Continue to flush gently until the emerging irrigant is clear. An optional final flush with sterile saline may be performed. Flushing with 1.5% NaOCl followed by 17% EDTA may be most beneficial.
Step 6	Using gentle suction, remove any remaining excess fluid. With the blunt ends of paper points, carefully dry the canal to the level of the working length.
Step 7	Some resources recommend placing a resorbable extraradicular barrier, such as calcium sulfate, through the apex. This provides a surface upon which to place the MTA or bioceramic material, 28 to prevent apical overfilling.
Step 8	Using an MTA or amalgam carrier form an MTA (or other bioceramic material) plug and gently tamp it at the apex using premeasured pluggers (with endodontic stop) or large bore paper points, until the apical 4-5 mm of the canal is filled. To reduce the risk of fracturing the tooth or extruding the material apically, select a plugger that does not bind on the sides of the canal. Placing the material apically can be performed in incremental steps, such as with multiple smaller plugs carefully moved to the apex, or potentially in one step with a longer carrier delivering a larger plug to the apex. To encourage flow and compaction of MTA to the apex, the plugger may be vibrated ultrasonically. Instrument options for forming and delivering plugs include retrograde amalgam carriers, the Micro-Apical Placement (MAP) System,e Messing gun,f Dovgan carrier,g or Lee MTA block and carver.h
Step 9	Remove excess material from the walls of the canal by flushing with sterile water. In a small tooth or near the crown access site, an ultrasonic scaler may also be used. Dry with paper points.
Step 10	From this point, the MTA or other bioceramic material may need only a short time to cure, depending on manufacturer's recommendations. If the curing time is short, or following some protocols,59,70 then endodontic obturation may follow immediately during the same procedure. If the required curing time is several hours, then a staged procedure may be indicated. In that case, the coronal aspect of the MTA plug is moistened using sterile water on a paper point, or a moist cotton pellet is placed over the MTA. Place a temporary restoration (CavitTM a, IRMTM b, glass-ionomer, or another temporary material). Recall the patient 4-6 h to 1 week later and acquire a dental radiograph to check for any changes. Remove the temporary restoration and cotton pellet, if present. Some investigators recommend flushing the canal again with dilute NaOCl followed by saline and drying with paper points in preparation for obturation.
Step 11	The working length is confirmed, and the tooth obturated and restored using conventional endodontic techniques.
Step 12	Clinical and radiographic follow-up for conventional endodontic therapy is recommended 6 and 12 months posttreatment, then annually for 5 years.21,65

Note. MTA, mineral trioxide aggregate.

As previously discussed, apexification has been used for years for the treatment of immature teeth with necrotic pulps in humans and animals but is falling out of favor in the human literature.^54,66,71 A recent veterinary review paper, citing many research studies showing successful regenerative endodontic therapy using dogs as models, proposed that these techniques also be considered in veterinary patients as an alternative to apexification or extraction. ⁶² Although apexification techniques create apical closure and allow for endodontic obturation, only limited additional root development occurs. ⁵⁸ On the other hand, regenerative endodontic therapy permits apical closure and potentially more significant development of root length and wall thickness.^58,60,72 A 2012 human retrospective study referred to as the Mahidol study found that with calcium hydroxide apexification, the root wall thickness increased 1.5% and the root length increased 0.4%; with MTA apexification, the root thickness increased 0.0% and the root length 6.1%; with regenerative therapies, the root thickness increased 28.2% and the root length 14.9%. ⁶⁰ A 2014 human retrospective study appreciated radiographically increased root development with regenerative endodontic therapy compared with apexification techniques, but the results were not found to be statistically significant. ⁶¹ Further, at 14 months posttreatment, the Mahidol study found 100% tooth survival in the regenerative endodontic therapy group, 95% in the MTA apexification group, and 77% in the calcium hydroxide apexification group, ⁶⁰ while the second study, with a 17-month follow-up, found no significant difference between the groups. ⁶¹ A 2017 human prospective study also found comparable clinical results (resolution of symptoms and apical healing) between apexification and regenerative endodontic therapy and found significantly increased root thickness and root length in the regenerative endodontic therapy group compared with the apexification group. ⁷² More prospective studies with larger case numbers and longer follow-up may clarify results.^61,72 Standardizing radiographic measurements between studies and using cone beam computed tomography (CBCT) for better 3D resolution and detail may also permit more accurate postoperative assessments ⁷² ; however, CBCT does cause increased radiation exposure for patients relative to dental radiography.^72,73

Several similar protocols have been described in the literature for regenerative endodontic therapy,^29,58,62,74 with the field likely to continue to evolve. The treatment is achieved in 2 visits. The first visit prepares and fills the canal with calcium hydroxide or triple antibiotic paste (TAP) in a similar process to that described for the first visit for calcium hydroxide apexification. TAP is traditionally made from a 1:1:1 ratio of ciprofloxacin:metronidazole:minocycline. The minocycline component of TAP has been associated with discoloration of crowns in human patients. ⁷⁴ If using TAP, resources have recommended sealing the pulp chamber with a dentin bonding agent to reduce the risk of coronal discoloration. ⁷⁴ Ensuring that the TAP remains below the CEJ may also reduce this risk. ⁷⁴ Another option is to use double antibiotic paste without the minocycline or to substitute another antibiotic for minocycline, instead of using conventional TAP. ⁷⁴ The second visit involves removing the calcium hydroxide or antibiotic paste from the prepared canal and inducing apical bleeding into the canal by overinstrumenting the canal 2 mm past the root end.^29,58,74 Alternatives to creating a blood clot include filling the canal with platelet-rich plasma (PRP), platelet-rich fibrin, or autologous fibrin matrix. ⁷⁴ Several studies in dogs found the best outcomes after using TAP for disinfection, followed by PRP as a scaffold.^75,76 Finally, an MTA or other bioceramic material barrier is placed followed by a glass ionomer, and the tooth is restored. ⁷⁴ The client should be counseled about the possibility of tooth discoloration even with successful treatment, and the potential use of medications or antibiotics during the procedure, in case of patient allergy. ⁷⁴

Treatment of nonvital immature teeth that have crown fractures utilizing regenerative endodontic therapy has been previously described^29,58,62,74 and is outlined in Table 6.

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Table 6.

Nonvital Immature Tooth with Crown Fracture: Protocol for Regenerative Endodontic Therapy.^29,58,62,74

Step 1	First Visit: Confirm lack of tooth vitality and open apex status via clinical examination and dental radiography.
Step 2	Ultrasonically scale the affected tooth and polish using fluoride-free pumice. Lavage the oral cavity with a 0.12% chlorhexidine solution. 53 Isolate the affected tooth using a rubber dam. Expand the sterile working area using sterile towels or drapes.
Step 3	Create an endodontic access if the fracture site does not allow for adequate straight-line access to the apical region of the tooth by an endodontic file.
Step 4	Carefully place an endodontic file to the apical limit. Determine the working length by stopping about 1 mm short of the root end, utilizing radiographs and setting an endodontic stop at this length, and avoiding trauma to the apical and periapical tissues.
Step 5	Place a closed-end, side-vented irrigation needle 1 mm from the root end. To prevent apical extrusion of irrigant, the irrigation needle must be small enough not to bind within the canal. Use copious, gentle irrigation with 1.5% NaOCl, ideally with a negative pressure irrigation system (EndoVac).i In human patients, at least 5 min of irrigation with 20 mL per canal is recommended. A large dog canine tooth will likely require longer flushing times and larger volumes. Continue to flush gently until the emerging irrigant is clear. The use final irrigation of sterile saline or 17% EDTA (5 min flushing time with EDTA was originally recommended, 2 min may retain positive effects but reduce cytotoxicity). 50
Step 6	Using gentle suction, remove any remaining excess fluid. Carefully dry the canal(s) with paper points.
Step 7	Fill the canal with calcium hydroxide paste or a low concentration (0.1-1 mg/mL) of triple antibiotic paste (TAP). Either a spiral paste filler or a syringe with an appropriately sized catheter attached may be used to reach the working length of the canal, backfilling the canal while slowly withdrawing the spiral paste filler or catheter tip.
Step 8	Take a dental radiograph to ensure complete filling of the canal to the working length. If voids are present, repeat Step 7.
Step 9	Place a temporary restoration (CavitTM a, IRMTM b, glass ionomer, or another temporary material).
Step 10	Second Visit: Recall the patient in 1-4 weeks. Evaluate the tooth for clinical or radiographic signs of infection, particularly appearance or increase in size of a periapical lucency, draining tract, or swelling. If signs persist, then redebride the canal, repeat treatment outlined in Steps 7-10, and consider oral antibiotic therapy.
Step 11	Isolate the affected tooth using a rubber dam.
Step 12	Gently and copiously irrigate the canals using 17% EDTA (2-5 min) to remove the intracanal medicament. An optional final flush with saline may be used (5 min flushing time with EDTA was originally recommended, 2 min may retain positive effects but reduce cytotoxicity). 50
Step 13	Apply gentle suction to remove any remaining liquid. Dry the canal with paper points.
Step 14	Induce bleeding in the canal by overinstrumenting the tooth 2 mm past the apical foramen/root end with a precurved hand file of small diameter. The entire canal system should fill with blood to the level of the cementoenamel junction. Using a moist paper point, stop bleeding approximately 7-9 mm from the coronal access site to allow adequate space for dressing and restoration.
Step 15	Optionally, a resorbable collagen matrix material (CollaPlug™, Collacote™, CollaTape™j) may be placed over the blood clot to provide stability/scaffolding for the following step.
Step 16	Place a 2-3 mm thick layer of MTA or other bioceramic material as a capping material over the blood clot or collagen matrix material.
Step 17	Gently flow 3-4 mm of glass ionomer over the capping material and light cure. If any glass ionomer restorative has adhered to the more coronal dentin walls, it should be gently debrided prior to preparation for the final restoration.
Step 18	Continue restoration of the tooth using standard restorative techniques.
Step 19	Recommendations for clinical and radiographic follow-up protocols in humans include visits at 3, 6, and 12 months, and then annually for at least 4-5 years.

Note. MTA, mineral trioxide aggregate.

Conclusion

The management of immature permanent teeth that have crown fractures presents a unique challenge in humans and animals because immature teeth often are presented with incomplete formation of the apices, thin dentin walls, and increased crown-to-root ratios. Losing pulp function during tooth development can be devastating for immature permanent teeth. Where possible, selection of the least invasive treatment option to permit ongoing tooth development is advisable. If unsuccessful, the treatment may progress to more invasive techniques. The ultimate goal in treating endodontically compromised immature permanent teeth is to preserve pulp vitality and continued dental development. Many established treatment options, including odontoplasty with bonding and sealing ± restoration, indirect pulp capping, vital pulp therapy, and apexification, have been utilized successfully for decades in the management of fractured immature teeth. These treatment options may also be applied to endodontically compromised mature permanent teeth, as well, but this paper has focused on treatments for immature teeth. Improvements in these techniques, such as employing MTA or other bioceramic materials for vital pulp therapy or for apexification, have improved success rates and decreased the number of appointments for patients. Regenerative endodontic therapy, a relatively new technique for treating nonvital immature teeth, has been used for years in humans but is now being recommended for animals. Although extraction is always a treatment option for any diseased tooth, modern therapies and improved success rates expand options for maintaining tooth health and retention. Veterinarians should be aware of all treatment options for the management of immature permanent teeth that have crown fractures so that they can properly educate their clientele, allowing for informed decision-making and timely referral for specialty veterinary dental care.

Materials