Abstract
A retrospective analysis of medical records from a specialty dental practice was performed, and all cases of full-coverage titanium alloy crowns of canine teeth in dogs were reviewed. Only 5 cases of failure were noted in a total of 53 crowns in 25 dogs. No bond failures between the prepared tooth and the crown were noted; all cases of failure were due to fracture of the tooth apical to the crown margin. The success rate of retention was 100% whereas the overall tooth survival was 91%. Risk factors for tooth fracture, such as crown height-to-diameter ratio, were identified.
Introduction
The use of crowns for the treatment of fractured teeth in veterinary medicine has been described in the literature for over 30 years. 1 A common concern among clients is the success rate of this procedure, following the significant financial investments, time out of work and training, and multiple anesthetic events associated with treatment. Multiple factors of crown preparation that influence success, including retention form, 2 surface area preparation, 3 and convergence angle, 4 have been well-described in the literature. Previous reviews of the success rate of crowns over the last several decades have shown rare instances of failure of treated teeth, 5 including an 85.3% success rate in 1 study; 6 however, newer adhesives may decrease the bond failure rate even further. A recent study using a feather margin preparation instead of a traditional chamfer margin showed an overall failure rate of 2.5%. 7 The goals of this case series were to assess the success rate of full-coverage crowns of the canine tooth performed with a chamfer margin and newer cements in a private practice setting while identifying the potential risk factors for failure.
Materials and Methods
A database search of the electronic medical record system of a multispecialty private veterinary hospital with a dentistry service was performed. The records of all crowns placed from January 2014 to January 2022 were obtained. These records were reviewed for tooth or teeth treated (including pathology), type of crown preparation, crown fabrication, materials used for cementation, and operator performing the preparation, impressions, and cementation. Data was collected for dog signalment, weight, and purpose as well as pathology of the occluding and contralateral teeth to evaluate for any potential contributing factors to crown failure. Each case was assessed as a success or failure based on the retention of the crown on the treated tooth without further pathology noted until patient death, loss to recommended follow-up (by phone or electronic mail), or at the time of manuscript submission.
All procedures were performed by either a board-certified veterinary dentist or a residency-trained veterinarian with practice limited to veterinary dentistry. All full-coverage canine tooth preparations were performed with chamfer margins 1 mm coronal to the gingival margin (with or without Type I or II crown-lengthening procedures), 8 and site-specific impressions were obtained with vinyl polysiloxane puttya and a light body washb. All materials were submitted to the same dental laboratoryc for fabrication of titanium alloy crowns (including sandblasting of the interior surface) and cemented under a separate anesthetic procedure 2 to 3 weeks later (depending on shipping time) following close inspection of the crown and prepared tooth for any abnormalities that could affect placement. All crowns were cemented with the same productd according to the manufacturer's instructions9,10 until January 2020, after which all crowns were cemented with the newer, improved formulation of the same producte.
Results
A total of 70 crowns in 33 individuals were extracted from the record system; 3 cases were excluded due to being maxillary fourth premolar crowns, and 14 cases were excluded due to being 3/4 coverage crowns of the canine tooth. A total of 53 full-coverage prosthetic crowns on canine teeth in 25 individual dogs were included. Twenty dogs were classified as working dogs, 19 of which were law enforcement (detection, protection, or multipurpose) and 1 of which was a medical assistance dog that served a handler who suffered from epilepsy. The remaining 5 dogs were pets, and 1 dog was trained to compete in bite sports.
The average age at time of crown fabrication and placement was 46 months (range 16-87 months) and the average weight of the dogs was 34.1 kg (range 23.7-44.9 kg). One of the dogs was an intact female, 2 were spayed females, 4 were neutered males, and the remaining 18 were intact males. One dog was a Dutch Shepherd, 8 were German Shepherds, 11 were Belgian Malinois, 2 were Doberman Pinschers, and 3 were various large Staffordshire Bull Terrier crosses.
The teeth represented were as follows: 14 right maxillary canine teeth, 16 left maxillary canine teeth, 12 left mandibular canine teeth, and 11 right mandibular canine teeth. Of these, 29 had had previous root canal therapy performed. The remaining 24 teeth were vital but had suffered loss of structural integrity of the crown due to abrasion or uncomplicated crown fractures. All dogs returned to their previous lifestyle and work following cementation of the prostheses.
None of the crowns were reported to have been lost due to bond failure between the prosthesis and tooth, but 5 out of 53 teeth (9%) in 3 out of 25 dogs (12%) did have complicated crown-root fractures occurring apical to the crown margin resulting in loss of the crown. All failures occurred in the vital teeth of dogs that worked in law enforcement. Loss occurred an average of 15 months following cementation (range 10-21 months); the individual dogs were 18, 37, and 50 months old at the time of crown preparation. No difference in the rate of failure between operators was noted.
Case 1
The first individual with crown failure was an 18-month-old, male, 29.7 kg Belgian Malinois used as a multipurpose law enforcement dog. He had been treated for multiple incisor fractures previously, although no enamel defects or other grossly abnormal teeth were noted on follow-up intraoral examinations and dental radiographs. He was presented due to a complicated crown fracture and significant loss of crown height of the right mandibular canine tooth that was treated with root canal therapy and full-coverage crown placement. Distal abrasion was noted on the remaining canine teeth at this time and full-coverage crowns were also placed. Two months later he was presented for surgical extraction of a complicated crown-root fracture of the right maxillary fourth premolar, at which time a full-coverage crown was placed on the contralateral maxillary fourth premolar. Twenty-one months after the initial crown placement on the canine teeth, he was examined due to a complicated crown-root fracture of the right maxillary and left mandibular canine teeth and, as noted above, the right mandibular canine tooth was shorter than the others due to previous fracture and root canal therapy. The right maxillary and left mandibular canine teeth were surgically extracted at this visit. This dog was humanely euthanized several years later due to significant behavioral changes, at which time the remaining left maxillary canine tooth and left maxillary fourth premolar with full-coverage crowns were intact.
Case 2
The second individual with crown failure was a 37-month-old, male, 40.6 kg Belgian Malinois who was used in law enforcement for scent detection. He was presented in order to receive crown placement on all 4 canine teeth due to distal abrasions. He had been treated 8 months prior due to a complicated crown fracture of a maxillary fourth premolar, at which time a crown was placed on that tooth following root canal therapy. At the time crowns were recommended to protect the damaged canine teeth. Eleven months following cementation of the crowns on the canine teeth, this dog was presented again due to a complicated crown-root fracture of the right mandibular canine tooth which was surgically removed using the open extraction technique. The dog was retired about a year later, at which time the remaining crowns were intact, and the dog was lost to follow-up.
Case 3
The third individual with crown failure was a 50-month-old, male, 37.5 kg Belgian Malinois in service as a multipurpose law enforcement dog. He was presented due to a complicated crown-root fracture of the left mandibular canine tooth, at which time significant distal abrasions of the remaining canine teeth were noted. The left mandibular canine tooth was surgically removed using the open extraction technique, and full-coverage titanium alloy crowns were recommended and placed as described previously on the maxillary canine teeth and the right mandibular canine tooth. Ten months later he was presented due to a complicated crown-root fracture of the right maxillary canine tooth which resulted in the loss of the crown of the tooth, and the remaining root was extracted at that time; both the contralateral left maxillary canine and occluding right mandibular canine teeth were intact with full-coverage crowns. Ankylosis of the root of the right maxillary canine tooth was noted clinically, and surgical removal using the open extraction technique was more difficult than anticipated. Two months later (12 months following placement, aged 62 months), he was presented again due to a complicated crown-root fracture of the left maxillary canine tooth; both the contralateral and occluding teeth had been previously extracted. Again, extraction of the left maxillary canine tooth was difficult due to ankylosis. The authors’ clinical assessment was that the high height-to-diameter ratio as well as the decreased elasticity of the periodontal ligament predisposed these teeth to fracture. At the time of manuscript submission, the remaining right mandibular canine tooth was intact with a full-coverage crown present.
Discussion
An uneven distribution in age, sex, weight, and breed of dogs, prevented conclusions from being drawn about predisposing factors of crown failure related to signalment. While all of the failures occurred in Belgian Malinois, that breed was also overrepresented in the treatment population. Other factors (e.g., these 3 individuals often trained together) could also influence the outcome. However, the patients most commonly presented clinically for crown placement are well-represented in this study. Additionally, since there were no bond failures noted, it is also difficult to draw any conclusions regarding potential differences in newer, fluoride-releasing cements that are dual cure versus the older formulations that did not contain fluoride and were self-curing.
No significant difference between tooth types that suffered crown failure was noted, but pathology or previous treatment of the contralateral or occluding teeth may have influenced the outcome. However, due to the relatively small number of failures, it was difficult to evaluate any significant trends in these cases. Certain risk factors were noted, such as the height-to-diameter ratio of the teeth, 11 deterioration of the periodontal ligament radiographically consistent with ankylosis, and use and training of the individual.
While all teeth with failed crowns were vital and their crowns were placed due to abrasion, it is the authors’ assertion that it was the height-to-diameter ratio rather than the vitality of the tooth that predisposed it to fracture. A previous study noted that in vitro studies of height-to-diameter ratio in unaltered canine teeth, showed a reduction of 10% to 20% which led to a decreased probability of fracture of 24.1% or 60.4%, respectively, but a 20% reduction also led to an increased probability of fracture of the contralateral tooth by 54.4%. 11 Teeth that have suffered crown fracture leading to root canal therapy and crown placement often are shorter, and vital teeth that have crowns placed due to distal abrasion often have a decreased diameter. It is uncertain as to whether crown reduction and endodontic treatment (either with root canal therapy or vital pulp therapy) should be considered in these cases. However, when additional treatment is performed, there is additional anesthesia time, cost, risk of failure, and need for follow-up as well as the concern of placing a full-coverage crown over a tooth that has received vital pulp therapy in case future root canal therapy is indicated.12,13 The contralateral teeth may then also be at increased risk of fracture. Individual risk factors such as age, animal use, and health of the other teeth should be considered when placing crowns on teeth that have an increased height-to-diameter ratio. Crown-lengthening procedures can also be performed to influence the base diameter of the tooth. 14
One of the most significant challenges to evaluating success, besides the uneven case distribution, is loss to follow-up. While annual evaluation under anesthesia along with professional dental cleaning is always recommended, there are many factors that may affect whether or not this occurs. Financial constraints in publicly owned working dogs, travel distance to qualified dental practitioners, loss of time in work or training, and transfer of dogs between handlers or jurisdictions can influence follow-up. Additionally, with a low complication rate, the owner or handler may perceive that follow-up is not indicated and thus decline recommended rechecks. When failure does occur, however, the veterinarian who placed the crown is often contacted due to the previous financial investments made in treatment.
Full-coverage crowns in canine teeth are highly successful when following previously described preparation techniques 8 and cementation.9,10 Loss of crown due to bond failure when using appropriate retention form, a dental laboratory familiar with fabricating crowns for veterinary patients, and the currently recommended adhesive cements are unlikely since no cases with this complication were reported. The overall success rate of 91% is acceptable for a recommendation of crown placement in working or pet dogs for treatment of endodontically treated or vital teeth, especially when other risk factors for fracture are taken into consideration.
Footnotes
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Materials
Express STD Putty, 3M ESPE, St. Paul, MN, USA. Express Light Body Wash (Regular Set), 3M ESPE, St. Paul, MN, USA. Precision Ceramics Dental Laboratory, Montclair, CA, USA. Panavia 21 Dental Adhesive Resin Cement, Kuraray, New York, NY, USA. Panavia F2.0 Dental Adhesive Resin Cement, Kuraray, New York, NY, USA.
