Recognition and Treatment of Endodontic Disease
Sandra Manfra Marretta, DVM, Diplomate ACVS, AVDC
The management of fractured teeth falls into the category of endodontic therapy. Endodontic therapy refers to the treatment of the diseased pulp of a tooth. The most common cause of diseased pulp in small animals is a fractured tooth. Any tooth in a dog or cat may be fractured. However, the most frequently fractured teeth in the dog are the canines, incisors and maxillary fourth premolars.
Fractured Teeth Versus Worn Teeth
Fractured teeth must be differentiated from worn teeth. The abnormal process of teeth wearing rapidly is known as dental attrition. Diet and chewing habits account for most cases of severe attrition. Pathologic grooming which may occur in severe cases of flea allergy can result in incisor teeth wearing down to the gingiva. The dental pulp responds to rapid wear by laying down secondary dentin, which is visible as a dark brown spot on the affected tooth. The dark brown spot is solid and cannot be entered with a dental explorer. No therapy is required in these cases. Occasionally, very rapid dental attrition can result in pulpal exposure. These cases require endodontic therapy.
Pulpal Exposure Versus No Pulpal Exposure
Dental fractures should be classified on presentation into two groups, fractures with pulpal exposure and fractures without pulpal exposure. A fracture of the enamel surface without exposure of the pulp requires only that the sharp edges of the fracture site be smoothed off as necessary to avoid any further oral trauma. A fractured tooth with exposed pulp requires endodontic therapy.
Pathophysiology of Fractured Teeth
Fractured teeth are often noted as an incidental finding on physical examination. However, a series of events may occur in some fractured teeth with exposed pulp which can result in significant clinical presentations. This series of events includes the following conditions: (1) exposed pulp, (2) bacterial pulpitis, (3) pulp necrosis, (4) apical granuloma, (5) periapical abscess, (6) acute alveolar periodontitis, (7) osteomyelitis, (8) sepsis.
The time required for this progression varies from months to years. When a tooth is fractured and the pulp is exposed the pulp will bleed. Pulpal exposure is extremely painful and animals with an acutely fractured tooth with pulpal exposure will hypersalivate, be reluctant to eat, and exhibit abnormal behavior. Over several months the pulp becomes necrotic and the animal is no longer painful until an inflammatory reaction occurs around the apex of the tooth at which time the animal becomes painful again. An endodontically diseased tooth is not only painful but it also is a potential source of infection for other parts of the body. An endodontically diseased tooth may present clinically as a discolored tooth which is painful on percussion. Soft tissue fistulas may occur secondary to endodontic disease. These fistulas are usually located above the mucogingival line. Endodontically diseased teeth may present with severe maxillary or mandibular swelling. Therefore, all endodontically diseased teeth should be either treated or extracted.
Several different endodontic procedures may be utilized to treat endodontically diseased teeth these techniques include: vital pulpotomy, conventional and surgical endodontic therapy. The most common and most successful type of endodontic therapy is conventional or nonsurgical endodontic therapy. Conventional endodontic therapy or nonsurgical endodontic therapy is performed through the crown of the tooth and is the most frequently performed endodontic therapy. This procedure is indicated whenever there is pulpal death of a tooth secondary to inflammation, infection or trauma. The purpose of root canal therapy is to preserve the function of the tooth while preventing it from causing adverse effects because of its presence. This is achieved by removing the necrotic or infected pulp and filling the pulp canal with an inert material. A properly performed root canal procedure will prevent infection or inflammatory products from extending from the tooth into the tissues that surround the apex of the tooth. There are several basic steps involved in performing conventional endodontic therapy. These steps include: (1) preparation, (2) access, (3) debridement, (4) drying, (5) filling, and (6) restoration.
Animals with a periapical abscess should be treated with antibiotics prior to treatment. The tooth should be disinfected with 0.2% chlorhexidine solution. A preoperative radiograph should be taken to identify landmarks and evaluate the postion and size of the canal(s), and the radiographic appearance of the apex and the periapical tissues.
Access to the pulp canal is made at a point that will permit straight delivery of the file to the apex of the tooth. A #1 round bur on a high speed handpiece can be utilized to create an access. One access is usually necessary for each canal. In certain fractures a straight access to the apex may be achieved through the coronal aspect of the fracture site. The preoperative films and if available a coronal access model should be utilized to determine the ideal access point(s).
Thorough debridement is an important part of endodontic therapy. The objective of debridement is to remove all pulpal tissue and to shape the canal for proper filling or obturation. There are several steps in the removal of pulpal tissue. These steps include: (1) removal of vital pulp tissue with a broach, (2) determination of working length, (3) enlargement and shaping of access, (4) filing of canal, (5) irrigation, and (6) recapitulation.
Removal of vital pulp tissue with a broach
Vital pulp tissue is removed from a canal by inserting the largest broach that will fit loosely in the canal without binding and twisting it greater than 360 degrees. The broach is then gently removed with the attached pulp tissue. This process may need to be repeated.
Determination of working length
A small file with a preplaced endodontic stop is inserted into the canal to the apex. A radiograph is taken to determine if the file did indeed reach the apex. Placement of the file is adjusted until the file is at the end of canal and at the apex but not through the apex as determined by a radiograph. The endodontic stop is then moved down the file until it contacts the crown while the end of the file is at the apex of the tooth. The file is then removed from the tooth and the distance from the tip of the file to the endodontic stop is measured. This distance becomes the working length of the file.
Enlargement and shaping of access
It may be necessary in some teeth with curved canals to shape the access site to achieve adequate access to the entire canal. Enlargement and shaping of the access site can be achieved with Gates Glidden drills. These drills are flame-shaped and tend to follow the path of the pre-existing hole and canal. They come in different sizes (#1-6). The size of the drill can be identified by the number of bands on the shaft. The smallest drill is used first and the hole is increased in size by working through the different sized drills. Caution must be utilized when using Gates Glidden drills because if they bind in the canal or are bent, the drill will break leaving the drill entrapped in the canal. The Gates Glidden drills are particularly helpful in shaping and enlarging the access of the canine teeth in dogs.
Filing of canal
The canal is debrided with files. Hedstrom files or K-files may be used to clean the canal. Hedstrom files are manufactured by cutting triangular pieces from a tapered wire. They are used in a push-pull manner. K-files are manufactured by twisting tapered wire, to produce cutting edges. They are more flexible than Hedstrom files. K-files are used in either push-pull or push-rotate clockwise 90 degrees and then pull movement. Files come in various lengths and sizes. The most frequently used files in veterinary dentistry are 25mm to 60mm in length. The proper length file is chosen based on the length of the pulp canal. The various sized files used in veterinary dentistry most frequently are #15 to #80. The #15 file is the smallest while the #80 is the largest. Filing begins with the smallest file and then they are used in sequential order, with each file inserted to the predetermined working length and drawn against each side of the canal. An EDTA preparation such as RC-Prep can be placed on the files or placed in the canal with a curved-tip syringe to soften the dentin and lubricate the files. Progressively larger files are introduced into the canal until the canal is thoroughly debrided. Thorough debridement is indicated by the presence of white dentinal shavings on the file and the absence of bleeding from the canal.
The canal is irrigated between each file size. Various irrigating solutions may be used to irrigate the canal. The most frequently used irrigating solution is 2.5% sodium hypochlorite solution (half strength bleach). Hydrogen peroxide may also be used to irrigate the canal. Final irrigation of the canal should be performed with sterile saline solution. When irrigating the canal a syringe with a blunt tipped needle should be utilized. The needle should be gently inserted into the canal approximately half way down the canal without binding. If the needle becomes lodged in the canal and the irrigant is forced into the canal the solution may be forced through the apex which will cause unnecessary pain postoperatively.
Periodically a smaller file should be placed into the canal to remove any dentinal shavings that might have become packed into the apical portion of the canal with the larger files.
The canal is dried using appropriately sized sterile paper points. Care should be taken not to insert the paper point past the apex. The canal is thoroughly dried when the inserted paper point comes out clean and dry. If the paper point has blood on it this is indicative of one of two things: (1) the paper point was inadvertently pushed through the apex, or (2) the canal is not thoroughly debrided and needs to be debrided further.
There are many different techniques for filling a canal. Most techniques involve the application of a sealer and then application of a solid filling material. The most frequently used sealers are zinc oxide and eugenol or AH-26. They can be placed in the canal with a spiral filler with a reduction gear on a slow-speed handpiece or injected into the canal. The solid material most frequently used to fill the canal is gutta percha. With the single-cone technique a dry gutta percha point the same size as the previously used last file is placed into the canal to the apex. A radiograph should be taken to access the ability of the single cone to fill the canal. The entire canal should be filled. When removing the dry gutta percha there should be slight resistance or "tugback" felt.
Alternatively, the lateral condensation technique may be utilized. With this technique a primary gutta percha point is placed in the canal and checked for a snug fit. A endodontic spreader that can reach 1-2mm from the apex is placed into the canal next to the primary gutta percha point. The spreader is rotated on its axis in a clockwise and counterclockwise direction multiple times and then removed. A gutta percha point slightly smaller than the spreader is quickly placed in the space caused by the spreader. The spreader is again introduced into the canal and another gutta percha point is inserted. This process is repeated until no more gutta percha points can be accommodated in the canal.
A relatively new technique has been successful in achieving an excellent endodontic fill is vertical condensation utilizing hot gutta percha. In this technique small amounts of hot gutta percha are placed on the end of a sterile file and rotated counterclockwise into the canal and then vertically condensed with a plugger. This process is repeated until the canal is adequately filled.
Restoration of the access site can be achieved with many different materials. The most commonly used materials include composites, glass ionomers, and amalgam. Restoration of the access site can be subdivided into four steps which include: (1) placement of an intermediate layer, (2) preparation of the surface, (3) placement of the restorative material, and (4) contouring or shaping and smoothing the restoration.
Placement of an intermediate layer
The endodontic filling should be protected from oral contamination. If strength is not a significant factor a reinforced zinc oxide and eugenol cement such as IRM can be used. It however must be covered by a layer of calcium hydroxide so that polymerization of the composite is not retarded by the eugenol if composite will be utilized in the final restoration. Alternatively zinc phosphate cement or glass ionomer may be used as an intermediate layer.
Preparation of the surface
Preparation of the surface includes creating a small undercut in the dentin with an inverted cone bur to provide a mechanical lock and removing all unsupported enamel with a chisel or sharp curette.
Placement of the restorative material
The manufacturer's instructions should be carefully followed when placing restorative materials. If amalgam is chosen as the restorative material it is mixed in the amalgamator and placed in the restoration site with an amalgam carrier and an amalgam plugger is used to condense the amalgam. If composite is chosen as the restorative material the enamel should be acid etched with 38-50% phosphoric acid gel for 30-60 seconds. The surface should be rinsed thoroughly then dried. The bonding agent is then applied according to the manufacturer's instructions. The final restorative agent or filled resin is applied. Glass ionomer may be used as the final restorative agent. Although not as strong as amalgam, glass ionomers have several unique properties that make it a good restorative agent . The tooth does not have to be acid etched to permit restoration retention. They also maintain a tight marginal seal. They release fluoride into the surrounding tooth structure. Glass ionomer like composite comes as a chemical cured or light cured material. It is important to follow the manufacturer's instructions when performing a glass ionomer restoration.
Contouring or shaping and smoothing the restoration
Following placement of the restorative material the restoration should be contoured or shaped. The final anatomic form of amalgam restorations is achieved with an amalgam carver. An amalgam restoration should be shaped from the tooth surface into the restoration to prevent "scooping" out the amalgam. The amalgam restoration is then burnished with a burnisher. Composite and glass ionomer restorations may be shaped and smoothed with finishing diamond burs or fine particle stones.
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