Radiographic Outcome of the Endodontic Treatment of 55 Fractured Canine Teeth in 43 Dogs (2013-2018)

Abstract

Medical records from 4 private practice veterinary dentistry specialty clinics were reviewed for a 5-year period (2013-2018) to identify dogs that had a fractured canine tooth treated by root canal therapy and returned for subsequent follow-up evaluation. Evaluation criteria included the presence of complete medical records with diagnostic quality intraoral radiographs for each procedure visit with a minimum of 6 months between visits. Forty-three dogs with a total of 55 endodontically treated canine teeth were identified and evaluated. Root canal treatment outcome was defined as successful, no evidence of failure (NEF), or failure based on radiographic findings. Patient age, time from initial treatment to follow-up, obturation material used, radiographic quality of obturation (including voids, overfill, and retention of fractured endodontic files), radiographic evidence of periapical disease and/or presence of external inflammatory root resorption (EIRR), and the presence or absence of a full coverage metal crown were evaluated. Treatment was classified as successful in 51 (92.73%) teeth, NEF in 3 (5.45%) teeth, and failure in 1 (1.82%) tooth. The results suggest that endodontic treatment of fractured canine teeth in dogs is a successful treatment option that allows for retention of this functionally important tooth.

Keywords

root canal therapy endodontic treatment complicated crown fracture canine tooth strategic tooth prosthodontic crown

Introduction

Traumatic tooth injury is a common presenting complaint in dogs, with a reported prevalence of 27% in the general population and a prevalence of 72.1% in patients presenting for maxillofacial injury.^1,2 The canine tooth is the most commonly fractured tooth and is more likely to have pulp involvement than any other tooth.^3,4 Complicated fractures, also termed enamel-dentin-pulp fractures, expose the pulp tissue and lead to irreversible pulpitis and loss of tooth vitality.^4–7 Treatment is required to prevent endodontic infection and pain, which may contribute to decreased quality of life and systemic disease.^4,5 Extraction or endodontic therapy are the only acceptable treatment options for teeth with complicated fractures.^6,7 Endodontic treatment is intended to allow for preservation of teeth with pulp disease.⁷

Due to their functional importance the canine, maxillary fourth premolar, and mandibular first molar teeth are referred to as “strategic teeth”. Extraction of the canine tooth in dogs decreases oral function, may require significant bone removal, and carries risk of significant complications including iatrogenic jaw fracture and formation of an oronasal fistula.⁸ In cases of oral injury resulting in chronic complicated crown fractures of strategic teeth, root canal treatment is preferred over extraction to maintain near-normal function and avoid surgical trauma.^7,9 In cases of acute pulp exposure, vital pulp therapy may be considered as an alternative to root canal therapy.^10,11 The long-term success rate of this treatment is highest for teeth that have been fractured less than 48 hours (88.2%).¹⁰ In the author's practice, treatment within this acute period is rarely possible.

The goal of root canal therapy is to clean, shape, disinfect, obturate and seal the pulp cavity.^7,9,12 This is a common procedure for many veterinary dentists and a low failure rate for this treatment has been reported in previous human and veterinary studies.^13–17 While previous veterinary studies exist, none are specific to the success rate of root canal treatment of fractured canine teeth in the dog using the obturation materials that are commonly used in veterinary dental practice. The purpose of this study was to evaluate and report the radiographic outcome of root canal treatment of fractured canine teeth in dogs.

Materials and Methods

Medical Records and Inclusion Criteria

A search of the medical and dental records at four private dentistry specialty practices was conducted to identify dogs that were diagnosed with complicated crown fracture(s) of canine teeth and received root canal treatment of these teeth over a 5-year period (2013-2018). Only dogs that had returned at least once for professional periodontal therapy with intraoral radiographs at least 6 months after the initial root canal treatment were included in the study. The most recent images were evaluated for any dogs that returned more than once during the study period. Additional criteria included the presence of diagnostic-quality intraoral radiographs for the time of treatment and for each follow-up visit, and the presence of complete medical and dental records including patient demographics. Teeth with radiographic or clinical evidence of significant periodontal disease and/or resorption (other than external inflammatory resorption due to endodontic disease) were excluded from the study.

The breed, age at presentation in months, sex, and neuter status were recorded. The medical and dental records were reviewed to determine the tooth affected, obturation material and method used, the time to follow-up examination in months, and the presence or absence of a full coverage metal crown. All radiographs as well as medical and dental records for patients that had multiple follow-up examinations were reviewed.

Radiographic Valuation and Diagnostic Criteria

Computed radiography (CR)^a or digital radiography (DR)^b was used. All radiographic images were reviewed by 3 evaluators, including 2 board certified veterinary dentists. The quality of obturation was evaluated for completeness. Voids in obturation were described as small if they were shorter than the width of the obturated pulp cavity and narrower than half the width of the obturated pulp cavity. All other voids were described as large. Overfill was recorded as present or absent, and described as the presence of any radiopaque obturation material in the periapical region. Periapical lesions (PAL) were defined as widening of the periodontal ligament space and were measured at their widest point. Widening was defined as the periodontal ligament space being focally more than two times greater than the width of the space at any other point around the root. All PAL were recorded as present or absent.

Root canal treatment outcome was defined as successful, no evidence of failure (NEF), or failure. While there is no consensus in the human literature on what defines “success” or “failure”,¹⁵ previous veterinary studies^13,14 evaluating endodontic treatment have used a modified version of radiographic criteria established by the European Society of Endodontology to define treatment outcome. For the purposes of this study, the treatment was defined successful if “the periapical periodontal ligament space was within reference limits upon follow-up examination and pretreatment external inflammatory root resorption (EIRR), if present, was unchanged in size on follow-up”. NEF was defined as “having stable EIRR and the periodontal ligament space width remaining the same or decreasing in size without completely returning to normal width”. Treatment failure was defined as “the development of EIRR or widening of the periodontal ligament space after treatment, or the worsening of existing EIRR or widening of the periodontal ligament space increased”.

Treatment Procedure

All root canal treatments were performed by diplomates of the American Veterinary Dental College or by a veterinary resident directly supervised by a diplomate. Crowns, when placed, were full coverage metal alloy crowns. The treatment methods used have been previously described in veterinary literature.^{3,6,7,9,12–14,18} All of the root canal treatments were completed in one visit.

Endodontic access was obtained via an access site created through the crown to allow for straight line access to the pulp canal. Instrumentation of the pulp cavity was achieved using hand files^c to establish working length, followed by nickel-titanium files^d on a rotary hand piece. The files were coated with an ethylenediaminetetraacetic acid (EDTA) gel^e designed to act as a lubricant and chelator. Sodium hypochlorite 6%^f was used to irrigate the canal between files to aid in cleaning, sterilization, and dissolution of debris. After instrumentation was complete, 17% EDTA^g was placed in the canal for 1 minute, rinsed with sterile saline, followed by a flush with 6% sodium hypochlorite. According to manufacturer specifications, a final sterile saline^h or alcohol rinseⁱ was performed for cases obturated with flowable gutta percha^j. The canal was then dried with sterile paper points^k. Methods of obturation included single cone gutta percha^l with flowable gutta percha^j, thermoplastic gutta percha (TGP)^m, and warm lateral compaction (WLC) of gutta percha with a root canal sealerⁿ. Access sites were restored with a glass ionomer^o intermediate layer and final composite resin^p restoration or with an unfilled resin bonding agent^q and composite resin restoration.

Statistical Analysis

Dependent variables assessed included patient age, time from initial treatment to follow-up, obturation material, obturation quality (individually assessed: presence of void, void size, void location, endodontic file separation, and overfill), presence of full-coverage metal crown, presence of EIRR, and presence of a PAL. Univariate ordinal logistic regression tests were performed on each variable and findings with p < 0.05 were considered statistically significant.

Results

A total of 55 root canal treatments in 43 patients met the study inclusion criteria. A total of 29 mandibular and 26 maxillary canine teeth were evaluated. The number of root canal treatments evaluated for each of the four canine teeth (left and right maxillary / left and right mandibular) was not significantly different. Age at the time of treatment ranged from 1 to 10 years (median 5 years). Time from initial treatment to radiographic follow-up ranged from 7 to 59 months (median 15 months) (Figure 1). Root canal treatment was successful in 51 (92.73%) teeth, NEF was found in 3 (5.45%) teeth, and treatment failed in 1 (1.82%) tooth. The median time to follow-up was longer for the failed case than for treatments that were successful and showed NEF. Age at initial treatment was not found to have a statistically significant impact on treatment outcome.

Obturation was performed using single-cone gutta percha with flowable gutta percha in 20/55 teeth (36.36%), with TGP in 34/55 teeth (61.82%), and by WLC of gutta percha with a root canal sealer in 1/55 tooth (1.82%). Obturation material was not significantly associated with increased risk of treatment failure (Figure 2), however, if a PAL was present at the time of treatment, this lesion was less likely to improve or resolve with TGP obturation (85% successful) than with single-cone gutta percha with flowable gutta percha (100% successful). The single case obturated by WLC did not exhibit a PAL at the time of treatment and therefore cannot be compared.

A small or large void in obturation was found in 12/55 (21.82%) and 4/55 (7.27%) teeth, respectively. No obturation material was found to be associated with an increased presence of a small or large void. The location of voids was evenly distributed (apical, middle, coronal) and the presence of a void was not associated with an increased rate of treatment failure. Overfill was found in 5/55 (9.09%) teeth (Figure 3). No specific obturation material was associated with a greater likelihood of overfill. Overfill was not found to be associated with an increased rate of treatment failure.

A radiographic PAL was found in 10/55 (18.18%) teeth and EIRR was diagnosed in 2/55 (3.64%) teeth at the time of treatment. Teeth with a PAL were more likely to be diagnosed as NEF or failure at follow-up examination (40% of cases) compared to teeth without a PAL at the time of root canal treatment (all cases successful). No relationship between the presence of EIRR alone at the time of treatment and outcome was found, and new EIRR was not diagnosed in any teeth at follow-up examination. The single failed root canal treatment had both EIRR and a PAL at the time of treatment, both of which worsened by the time of follow-up examination. No other teeth had both EIRR and a PAL at the time of treatment.

A total of 32/55 (58.18%) teeth had a full coverage crown placed in conjunction with root canal treatment (Figure 4). The outcome for teeth with crowns compared to teeth without crowns was not different overall, however, the subset of teeth with a PAL that had a crown placed were more likely to recover from the PAL and be diagnosed as successful upon follow-up (71.42% successful) than teeth with a PAL and no crown (33% successful). No teeth with crowns had EIRR at the time of treatment.

A small piece of the tip of the rotary file separated and was subsequently retained within the obturation material in 4/56 (7.14%) of treated teeth (Figure 5). All of the retained file tips were less than 1.2 mm in diameter and appeared entombed within the obturation material on radiographic evaluation. None of these 4 teeth had EIRR at the time of treatment and 1 had a PAL, which was improved at the time of follow-up examination. Time to follow-up examination was not significantly different for this group than for the study population.

Discussion

Endodontic treatment of fractured canine teeth in dogs provides the best long-term outcome for the patient and should be recommended over extraction when fracture of this tooth results in pulp exposure.^7–9,12 Assessment of root canal therapy in 55 canine teeth found that treatment was successful or showed NEF in 54 (98.18%) teeth. Age at the time of treatment, the obturation material used, the presence of a void, the presence of overfill, the placement of a full coverage crown, and the presence of EIRR (without concurrent PAL) were not found to have a statistically significant influence on treatment outcome.

The median time to follow-up examination was longer for the failed treatment compared to the follow-up time for successful treatments and those showing NEF. This result has low statistical power due to the small sample size of failed treatments (n = 1) and therefore meaningful evaluation of time to follow-up on treatment outcome is not possible in this study population. No significant difference in time to follow-up was found between successful treatment and those with NEF. This is consistent with a previous assessment of root canal treatment outcome in dogs that also concluded there is not a relationship between follow-up time and outcome.¹⁴

Periapical infection is often the presumptive diagnosis for a radiographic periapical lesion associated with fractured teeth, however, infectious, inflammatory, neoplastic, and idiopathic etiologies are possible.¹⁹ Histopathological analysis of the periapical tissues is needed to definitively determine the etiology of these lesions, which is rarely performed in practice unless there is clinical suspicion for neoplasia. As all of the teeth evaluated in this study were fractured and had clinically evident macroscopic pulp exposure, we assume that there was microbial invasion into the pulp chamber and periapical infection with inflammation is the most likely etiology for the radiographic PAL. Consistent with previous studies in both humans and dogs, teeth with a PAL at the time of treatment were significantly less likely to be classified as successful upon follow-up than teeth without a PAL.^14–17

Interestingly, dogs that had a PAL at the time of root canal treatment and had a full coverage metal crown placed were significantly more likely to have the PAL resolve than dogs without a crown. This may be due to the improved coronal seal provided by a full coverage crown versus restoration alone, as the crown and crown cement material provide an additional layer over the restored fracture and access sites. Previous studies in dogs and humans demonstrate that the quality of the coronal restoration is one of the most important operative factors contributing to endodontic treatment success.^15,16,20,21 No overall difference in outcome between teeth with and without crowns was found, attributed to the fact that many of the teeth with crowns did not have a PAL at the time of treatment. Thus, only this smaller subset of crowned teeth with a PAL were found to have a different outcome.

While the presence of EIRR alone was not associated with outcome, the only case diagnosed with both EIRR and a PAL at the time of initial treatment had a poor outcome (treatment failure). Both the EIRR and PAL worsened from the time of treatment to follow up in this dog. The small sample size (n = 1) does not allow for meaningful statistical analysis, however, this specific combination of pathology may be a risk factor for treatment failure and further evaluation is warranted. It is important to note that this dog with radiographic treatment failure did not exhibit any clinical signs of pain and presented only for routine annual professional dentistry.

Our results indicate that obturation material and quality of obturation does not impact treatment outcome. To the author's knowledge, only one study specifically evaluating obturation in dogs exists, which also found no difference in endodontic treatment outcome related to obturation.²⁰ Additionally, apical dye leakage studies evaluating the obturation materials used in our study population found no difference in apical seal between each.^22,23 When grouped by obturation material, the overall presence, size, and location of voids was similar for all teeth. Thus, while likely not a significant risk factor for treatment failure, the endodontically treated teeth in this study shared the same hypothetical risk of apical leakage.

Instrument fracture or separation is a known complication of endodontic treatment with a reported incidence of up to 6% in humans.^15,24,25 While there are studies evaluating the impact of instrument separation on outcome in humans, review of the veterinary literature at the time of publication did not reveal any investigation of this complication in dogs. File separation with intra-canal retention of the file segment occurred in 4/56 (7.14%) of dogs and had no impact on treatment outcome. In humans, the likelihood of treatment failure resulting from instrument separation is reported to be low if appropriate instrumentation and sterilization is not impeded by the retained file segment.^24,25 In the 4 cases where file separation occurred the retained file segment did not obstruct the canal and therefore did not meaningfully interfere with any additional instrumentation or sterilization. In every case of file separation reported, complete obturation with radiographic entombment of the file segment was achieved.

While our reported rate of file separation (7.14%) is higher than what is reported in the human literature, we hypothesize that this complication is over-represented in this study population versus the total population of dogs receiving endodontic treatment of a canine tooth during the study period. In our practice, 1-year radiographic follow-up is recommended for all patients receiving endodontic treatment, however, as a specialty referral hospital, many of our patients choose to return to their referring veterinarians for routine annual professional dental care. When file separation occurred, clients were informed of this complication, informed that it could impact treatment outcome, and were strongly encouraged to return to our practice for follow-up evaluation in case the need for additional treatment such as surgical endodontic treatment is found. Because they are informed of these factors, we hypothesize that these clients are more likely to return to our practice for follow-up than the average client.

The primary limitation of this study is the large number of patients that were lost to follow-up. This limitation is inherent to retrospective investigations in the veterinary field, and the 55 teeth presently evaluated represent only 7% of the total dog canine teeth that received endodontic treatment during the study period. It is also important to consider that pathology associated with endodontic disease and/or failed endodontic treatment may be under-diagnosed using intraoral radiography alone.²⁶ Investigation of periapical pathology in endodontically treated teeth using cone beam computed tomography (CBCT) has shown to be more sensitive than intraoral radiography,²⁷ and further studies using this imaging modality are indicated. The results of this study confirm that endodontic treatment is the preferred treatment for complicated crown fractures of the canine tooth in dogs.

Materials

CR7 Vet, iM3, Vancouver, WA

Schick 33, Sirona Dental, Long Island City, NY

Endoflex, Henry Schein, Melville, NY

LightSpeed LSX NiTi rotary files, Discuss Dental, San Antonio, TX

RC Prep, Premier Dental Products, Plymouth Meeting, PA

Sodium Hypochlorite Solution 6%, Henry Schein, Melville, NY

EDTA Solution 17%, Henry Schein, Melville, NY

Sterile Saline Solution, Aspen Veterinary Resources, Frand Island, NY

70% Isopropyl Rubbing Alcohol, Henry Schein, Melville, NY

GuttaFlow 2, Coltene/Whaledent, Mahwah, NJ

Absorbent Paper Points, Shipps Dental and Specialty Products, Marana, AZ

Gutta Percha Points, Shipps Dental and Specialty Products, Marana, AZ

Calamus, Dentsply, York, PA

AH Plus, Dentsply, York, PA

Ionoseal, VOCO, Cuxhaven, Germany

Filtek Supreme, 3M, Saint Paul, MN

Scotchbond Universal Adhesive, 3M, Saint Paul, MN

Footnotes

Acknowledgements

The authors would like to thank Curt Coffman, DVM, DAVDC for his contributions to study design and final manuscript review.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Alexander I. Adrian

References

Golden

Stoller

Harvey

. A survey of oral and dental disease in dogs anesthetized at a veterinary hospital. J Am Anim Hosp Assoc. 1982;18(6):891‐899.

Soukup

Mulherin

Snyder

. Prevalence and nature of dentoalveolar injuries among patients with maxillofacial fractures. J Small Anim Pract. 2013;54(1):9‐14.

Capik

Ledecky

Sevcik

. Tooth fracture evaluation and endodontic treatment in dogs. Acta Vet Brno. 2000;69(2):115‐122. doi:10.2754/avb200069020115

Soukup

Hetzel

Paul

. Classification and epidemiology of traumatic dentoalveolar injuries in dogs and cats: 952 injuries in 660 patient visits (2004-2012). J Vet Dent. 2015;32(1):6‐14. doi:10.1177/089875641503200101

Soukup

. Traumatic dentoalveolar injuries. In: Lobprise

Dodd

, eds. Wigg‘s Veterinary Dentistry Principles and Practice. 2nd ed. Wiley-Blackwell; 2019: 109‐130.

Niemiec

. Fundamentals of endodontics. Vet Clin North Am Small Anim Pract. 2005;35(4):837‐868. doi:10.1016/j.cvsm.2005.03.001

Boyd

. Basic endodontic therapy. In: Lobprise

Dodd

, eds. Wigg‘s Veterinary Dentistry Principles and Practice. 2nd ed. Wiley-Blackwell; 2019: 311‐334.

Verstraete

FJM

Lommer

Tsugawa

. Extraction of canine teeth in dogs. In: Verstraete

FJM

Lommer

, eds. Oral and Maxillofacial Surgery in Dogs and Cats. Saunders Elsevier; 2012:121‐129.

Girard

Southern

Hennet

. Root canal treatment in dogs and cats. J Vet Dent. 2006;23(3):148‐160. doi:10.1177/089875640602300304

10.

Clarke

. Vital pulp therapy for complicated crown fracture of permanent canine teeth in dogs: a three-year retrospective study. J Vet Dent. 2001;18(3):117‐121. doi:10.1177/089875640101800301

11.

Karabucak

Lim

Iqbal

. Vital pulp therapy with mineral trioxide aggregate. Dent Traumatol. 2005;21(4):240‐243. doi:10.1111/j.1600-9657.2005.00306.x

12.

Clarke

. Endodontics of dogs and cats: an alternative to extraction. Aust Vet J. 1995;72(10):383‐389. doi:10.1111/j.1751-0813.1995.tb06176.x

13.

Strom

Arzi

Lommer

Fulton Scanlan

Kass

Verstraete

FJM

. Radiographic outcome of root canal treatment of canine teeth in cats: 32 cases (1998-2016). J Am Vet Med Assoc. 2018;252(5):572‐580. doi:10.2460/javma.252.5.572

14.

Kuntsi-Vaattovaara

Verstraete

FJM

Kass

. Results of root canal treatment in dogs: 127 cases (1995-2000). J Am Vet Med Assoc. 2002;220(6):775‐780. doi:10.2460/javma.2002.220.775

15.

Tabassum

Khan

. Failure of endodontic treatment: the usual suspects. Eur J Dent. 2016;10(1):144‐147. doi:10.4103/1305-7456.175682

16.

Smith

Setchell

Harty

. Factors influencing the success of conventional root canal therapy- a five year retrospective study. Int Endod J. 1993;26(6):321‐333. doi:10.1111/j.1365-2591.1993.tb00765.x

17.

Mann

Rahbaran

Lewsey

Gulabivala

. Outcome of primary root canal treatment: systematic review of the literature- part 2. Influence of clinical factors. Int Endod J. 2008;41(1):6‐31.

18.

Coffman

Visser

. Tooth preparation and impression for full metal crown restoration. J Vet Dent. 2007;24(1):59‐65. doi:10.1177/089875640702400113

19.

Menzies

Reiter

Lewis

. Assessment of apical periodontitis in dogs and humans: a review. J Vet Dent. 2014;31(1):8‐21. doi:10.1177/089875641403100101

20.

Sabeti

Nekofar

Motahhary

Ghandi

Simon

. Healing of apical periodontitis after endodontic treatment with and without obturation in dogs. J Endod. 2006;32(7):628‐633. doi:10.1016/j.joen.2005.12.014

21.

Ray

Trope

. Periapical status of endodontically treated teeth in relation to the technical quality of the root filling and the coronal restoration. Int Endod J. 1995;28(1):12‐18. doi:10.1111/j.1365-2591.1995.tb00150.x

22.

Lothamer

Anderson

Hetzel

, et al. Apical microleakage in root canals obturated with 2 different endodontic sealer systems in canine teeth of dogs. J Vet Dent. 2017;34(2):86‐91. doi:10.1177/0898756417713978

23.

Krug

Manfra Marietta

Thomas

Perrone

. Comparison of cold GP/sealer and resin bonded obturation techniques in canine teeth in dogs. J Vet Dent. 2008;25(1):10‐14. doi:10.1177/089875640802500105

24.

Spili

Parashos

Messer

. The impact of instrument fracture on outcome of endodontic treatment. J Endod. 2005;31(12):845‐850. doi:10.1097/01.don.0000164127.62864.7c

25.

Simon

Machtou

Tomson

Adams

Lumley

. Influence of fractured instruments on the success rate of endodontic treatment. Dent Update. 2008;35(3):172‐179. doi:10.12968/denu.2008.35.3.172

26.

Garcia de Paula-Silva

Santamaria

Leonardo

, et al. Cone-beam computerized tomographic, radiographic, and histologic evaluation of periapical repair in Dogs’ post-endodontic treatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2009;108(5):796‐805. doi:10.1016/j.tripleo.2009.06.016

27.

Garcia de Paula-Silva

Hassan

Bezerra da Silva

, et al. Outcome of root canal treatment in dogs determined by periapical radiography and cone-beam computed tomography scans. J Endod. 2009;35(5):723‐726. doi:10.1016/j.joen.2009.01.023