**This is a brand new presentation that is in development and is as yet incomplete. It includes a review of indications for crown therapy in dogs (and cats), recommended materials, as well as presentation and discussion of the feather margin (or knife edge) techniques for tooth preparation. It references and builds on the information included in: Success of Feather Margin Preparation for Full Metal Prosthodontic Crowns in the Canine Teeth in 84 Pet and Working Dogs (2005-2017) J Vet Dent. 2022 Mar;39(1):34-40.
Crown therapy has become a widely accepted treatment option for teeth in canine patients. Indications for prosthodontic crown therapy include teeth that have been worn through attrition or abrasion, or fractured, as well as the teeth of working dogs, or dogs with behavioral predispositions to excessive or potentially damaging use of their teeth (for example, habitual cage chewers, or highly reactive or anxious individuals). Working dogs, particularly those used in bite work, are frequent candidates for prosthodontic crown therapy. Affected teeth may or may not have been previously treated by root canal therapy.
Fractured teeth are frequently encountered issue in small animal practice. Little data is available on the prevalence of traumatic dentoalveolar injuries (TDI), (which includes luxation as well as other dental injuries), in dogs and cats. Reportedly, 26.2% of dogs and cats have at least one TDI, and crown fractures constitute four-fifths of all TDI in dogs and cats. In addition to tooth fracture, abrasive damage, behavioral characteristics, training and/or work-related causes may also be indications for prosthodontic crown treatment. A prosthodontic crown is a cemented extra-coronal restoration that covers the entire surface of the clinical crown. Crowns are indicated to protect and strengthen weakened teeth, and to restore function.
There are three types of margin commonly used in veterinary crown preparation: bevel, chamfer, and 90 degree (shoulder). In our practice, we aim to routinely use a ‘feather’ or ‘knife edge’ margin technique rather than the more commonly employed and widely accepted ‘chamfer’ margin for preparation of canine teeth in both dogs and cats. Personal preference (eg. bur choice) plays a significant role in crown preparation, but in general, a chamfer margin is created by first using a round diamond bur around the circumference of the tooth just above the gingival margin, cutting into the enamel to a depth of 0.5-1.0 mm. The primary characteristic of the chamfer margin is the rounded internal line angle created with the round diamond bur as described above. Shoulder margins, or 90 degree margins, are recommended for porcelain fused to metal (PFM) restorations, and may be created with a flat-end cylinder diamond bur. The axial portions of the tooth are then removed to the depth of the margin and shaped to create a smooth preparation, with no unsupported enamel nor undercuts.
Any margin angle other than 90 degrees is considered a bevel. The feather margin is a bevel margin of greater than 70 degrees. Anecdotally, feather preparations are faster and easier to perform, take impressions of, and finish, and because less tooth structure is removed in this preparation the remaining tooth is stronger and more resistant to fracture.
Crown preparation should remove as little enamel and/or dentin as is necessary, allowing space for a prosthodontic crown to fit without contacting other teeth, and eliminating enamel undercuts. Enamel in dogs is inconsistent, varying from 0.1-0.6 mm across a tooth, and the cervical bulge is an area of tooth thickening, not thicker enamel.
When performing feather margin crown preparations, it is not uncommon for the entire preparation to remain within the enamel layer, retaining even greater amounts of tooth structure than preparations extending into the dentin layer. In canine teeth, it is most vital to remove sufficient tooth structure for the prosthetic crown in occlusal areas (the mesial aspect of the maxillary canine teeth, and the mesial and distal aspects of the mandibular canines) to avoid contact between the metal crown and opposing canines and incisors. In non-occlusal areas of the canines, there is generally enough space to allow for minimal enamel removal, even though it may result in a metal crown slightly thicker or larger in these areas than the original, anatomic tooth. Without question, each patient must be thoroughly evaluated for bite, tooth spacing, and any preexisting malocclusion, and canine teeth prepared for prosthetic crowns that will comfortably accommodate an individual animal’s anatomy. A study published in 2022 showed that feather preparation is as least as successful as the chamfer margin preparation most commonly taught and performed in veterinary prosthodontics.
Typical failures for prosthodontic crown procedures in veterinary patients include fracture apical to the crown, and bond failure, and occur in teeth prepared with chamfer and shoulder margins as well as feather or knife margins. Failure by wearing through a metal crown is extremely rare or unreported.
As veterinary dentistry matures and gains recognition in the pet-owning population, prosthodontic crown therapy will also continue to grow. Our ability to successfully apply proper planning and treatment must grow as well. Much work has been done in recent years to improve the quality and quantity of evidence-based research available on the subject.
The feather preparation is the most conservative of all margin preparation techniques, and may remain completely within enamel layers, without extending into dentin; it is therefore possible that significant surface area is retained. Additionally, by not exposing dentinal layers, it may be presumed that the prepared tooth is less sensitive, leading to less patient discomfort while awaiting crown manufacture and cementation.
