Endodontic Instruments for Root Canal Therapy

Endodontic Instruments for Root Canal Therapy Kenneth F. Lyon, DVM, Dipl AVDC

This article on endodontic instrumentation includes endodontic instruments and techniques of root-canal preparation of teeth in veterinary patients. Familiarity with instruments covered in this article and with advances in veterinary endodontics has become necessary for the veterinary dental practitioner who wishes to practice dentistry using current techniques. Veterinary endodontic techniques that help to retain the teeth longer are increasing in demand as an option to extracting damaged teeth. Endodontic treatment involves removal of the irreversibly damaged pulp, followed by cleaning and shaping of the root canal space using endodontic instruments and subsequent filling, or obturation, with a semisolid material and a sealer. Copyright © 2001 by W.B. Saunders Company

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ndodontlcs is defined as the branch of dental science concerned with the study of form, function, health of, injuries to, and diseases of the dental pulp and periradicular region and their treatment. Endodontic treatment includes any procedure designed to maintain the health of all, or part of, the pulp. When the pulp is diseased or injured, treatment is aimed at maintaining or restoring the health of the periradicular tissues, usually by root-canal treatment, but occasionally in combination with endodontic surgery. Endodontic techniques have been recently published for veterinary patients. 1 Standard root canal therapy is more clearly described as conventional endodontics. Most modern endodontic treatment involves removal of the irreversibly damaged pulp, followed by cleaning and shaping of the root canal space and subsequent filling, or obturation, with a semisolid material and a sealer. 2-33 Shaping of the canal is performed by either hand or engine-driven instruments, the latter including sonically and ultrasonically powered files and handpieces with rotating, randomly vibrating, or reciprocating actions. Cleaning is performed by irrigating the canal system with one of a number of solutions that may be antibacterial and have tissue-dissolving ability. Obturation is achieved with gutta percha and a rootcanal sealer. The cleaning and shaping phase of endodontic treatment is regarded as the most important. When the canal is clean, it is important that microorganisms do not recontaminate the system. Because of the complex anatomy of the root-canal system, complete disinfection is almost impossible to achieve. It is important, therefore, that any remaining microorganisms in the dentinal tubules are prevented from multiplying by the use of

From the Mesa Veterinary Hospital, Department of Dentistry, Mesa, AZ; and the Southwest Veterinary Specialty Center, Tucson, AZ. Address reprint requests to Kenneth F. Lyon, DVM, Department of Dentistry, Mesa Veterinary Hospital, 858 North Country Club Drive, Mesa, AZ 85201. Copyright © 2001 by W.B. Saunders Company 1096-2867/01/1603-0003535.00/0 doi: 10.1053/svms.2001.28166

an antimicrobial dressing, followed by 3-dimensional filling. Recontamination from the oral cavity must be avoided, and the importance of a good coronal seal cannot be overestimated. A general increase in awareness of the benefits of veterinary dental care has created a rise in the demand for procedures that help to retain the teeth longer. 34 Periradicular lesions are often undiagnosed or untreated. 35 A rational approach to the treatment of disease requires an understanding of the pathologic process, which in turn demands a knowledge of the normal anatomy and physiology of the tissues involved. = Once the veterinary dental practitioner develops this awareness, then the focus shifts to treatment of the endodontic system. The most important phase of developing endodontic skills requires the veterinary dental practitioner to become familiar with most of the endodontic instruments that are available to make clinical decisions about which instruments are appropriate for root canal therapy.

Endodontic Instruments There are many different types of instruments used for endodontic procedures. There are hand-operated instruments and machine-driven instruments. There are rotary instruments and instruments for root canal obturation. Most endodontic instruments have been standardized to improve quality and to reduce endodontic failure. The International Standards Organization (ISO) working with the Federation Dentaire Intemationale (FDI) in the Technical Committee 106 Joint Working Group (TC-106 JWG-1) established the international standards for endodontic instruments. The American National Standards Institute (ANSI) and its Committee Z-156 (Dentistry), which was later designated Committee MD-156 (Medical Devices), independently developed American standards. In 1976, the American National Standard (Specification no. 28) was adopted. This set the standard for shape, dimensions, and diameter of root canal instruments. In 1981, the American Dental Association (ADA) Council on Dental Materials, Instruments, and Equipment, along with ANSI, adopted Specification number 28 for the H-type instruments. These newer guidelines are referred to as the Standard specifications and the early guidelines are referred to as the Conventional specifications. The ISO and FDI Joint Working Group placed endodontic instruments into groups according to use. There are two ISO/ FDI standards pertaining to instruments. ISO/FDI No. 3630/1 deals with K-type files (ANSI/ADA No. 28), Hedstrom files (ANSI/ADA No. 58), and barbed broaches and rasps (ANSI/ ADA No. 63). ISO/FDI No. 3630/3 deals with condensers, pluggers, and spreaders (ANSI/ADA No. 71). I n s t r u m e n t Groups By Use The easiest method to understand endodontic instruments is to place them into the groups that the ISO/FDI Joint Working

Clinical Techmques in Small Animal Practice, Vol 16, No 3 (August), 2001: pp 139-150

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Group established. There are 4 groups distinct in the types of endodontic instruments that are described.

Group I: Endodontic instruments. Hand/finger-operated use only. These instruments include Ktype reamers and files, H-type files, R-type rasps, barbed broaches, probes, applicators, filling pluggers or condensers, and filling spreaders.

Group II: Endodontic instruments. Engine-driven; low-speed two-part shaft and operative head. These instruments are designed for use in straight, contraangle, or specially designed endodontic contra-angle handpieces. The operative heads are identical to those in Group I, but with the handles replaced with attachments for a latch-type handpiece, or specially designed instruments. These include K-type reamers and files, H-type files, R-type rasps, B-2 reamers, quarter-turn reamers, and paste carriers (lentulo spiral fillers).

Group III: Endodontic instruments. Engine-driven; one-part shaft and operauve head. This group includes B-1 reamers, G-type reamers (Gates-Glidden), P-type reamers (Peeso), A-type reamers, D-type reamers, O-type reamers, K-type reamers, T-type reamers, M-type reamers, and root facers. These instruments include the low-speed instruments in which the latch type of attachment is in one piece with the working part. Rotary instruments like Profile, LightSpeed, Quantec, POW-R, and Hero 624, although not standardized, could be included in this group.

Group IV: Endodontic points. This group includes all types of filling points (gutta percha points and silver points), as well as absorbent paper points.

Hand Instruments All of the endodontic hand instruments are different from their regular dentistry counterparts. The endodontic explorer has two straight and very sharp ends angled in two different directions from the long axis of the instrument. Several types of endodontic spoons are available that have a much longer offset from the long axis than regular spoons, for better reach. These are intended for sharp pulp tissue excision. The locking pliers with grooves for holding paper and gutta percha points is an important instrument for rapid and secure transfer during endodontic procedures and is superior to the College or Perry pliers for working with points.

Hand/Finger-Operated Endodontic Instruments This group of instruments includes all the instruments that are commonly called files, including barbed broaches, rasps, Ktype files, and Hedstr6m files. The barbed broach and rasp are the oldest endodontic intracanal instruments still being produced. These instruments differ in taper and barb size. The broach has a taper of 0.007 to 0.010 mm/mm and a rasp of 0.015 to 0.020 mm/mm. The barb height is much larger in the broach than in the rasp. The broach is much weaker than the rasp, and both were designed to extract pulp tissue from the root canal.

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Vital pulps, low in collagen, are very difficult to remove with a broach. The K-type file and reamer (originally from Kerr Manufacturing Company in i915) are the oldest useful instruments for cutting and machining dentin. The instruments are made from a steel wire that is shaped into a tapered square or mangle in cross-section. This wire is twisted to generate a file or reamer. A file has more flutes per length unit than a reamer. The reamer that is less twisted is more flexible than a comparable file. The K-type file works by crushing the dentin when turned into a canal. The apical enlargement of the canal is not an abrasive action, but a compression-and-release destruction of the dentin surrounding the canal. The K-type file does not thread itself deep into dentin because of dull flutes and shallow concavities between flutes. The K-type file is strong and is effective in removing dentin because of more space between flutes. The working motion (rotation and pull) used in a reaming motion causes very little transport of the root canal, and the instrument tends to be stay self-centered in the canal. When used in a counterclockwise rotation, breakage occurs in half or less of the rotation required for breaking in a clockwise rotation. When used in a counterclockwise rotation, the instrument should be operated carefully. The H-type instrument is a more aggressive instrument than the K-type instrument. The H-type instrument (Hedstrtm) is manufactured by using computer-assisted machining technology that cuts the files from a round blank. This technique makes it possible to adjust the rake angle and the helical angle. The edge facing the handle can be made very sharp. These files machine the root canal wall as the instrument is pulled, but have no abrasive action when pushed. This file will self-thread into the root canal walls when turned clockwise. It may enter the dentin and then fracture when attempting to unscrew or pull out. This rarely happens with a K-type file. An H-type file is ideal for bulk removal of dentin, but less useful for reaming a root canal. The Hedstrtm file is difficult to bend to the desired curvature without creating sharp nicks. The instrument will break when cracks develop in the file. Hybrid instruments are modifications of the H-type and Ktype files. They are not often standardized and have different shaft shapes (ie, rhomboid), or the files are made with computer-assisted grinding using round blanks. Double-helix H-files have double the machining edges, but these may not increase efficiency because the edge spacing is decreased and they may separate more easily.

Engine-Operated Endodontic Instruments Rotary instruments, which are engine-driven, have become more available and reliable since the advent of nitinol, an alloy of NiTi. There are 5 major instruments available: ProFile and ProFile GT (Tulsa Dental Products, Tulsa, OK), LightSpeed (Light Speed Technology, Inc, San Antonio, TX), Quantec (Analytic, Orange, CA), POW-R (Union Broach, York, PA), and Hero 642 (MicroMega, Geneva, Switzerland). The ProFile, LightSpeed, and Quantec files are similar in design with Ugrooves and radial lands that prevent cutting into the root-canal walls, causing premature fractures, perforations, and transportation. The land also gives the file significant strength because it has a larger peripheral mass. The peripheral strengthening has been further accentuated in the Quantec instrument. The newest is the Hero 642, which has a trihelical Hedstrom design with KENNETH F. LYON

sharp flutes. Because of the progressively changing helical angle for the flutes, there is less risk for binding in the root canal. Rotary NiTi instruments require constant speed to prevent stress fractures. It is highly recommended that an electric handpiece be used, because the speed can be maintained more evenly at the correct rpm. The rotary shaping instruments have the benefit of flexibility and have reduced the incidence of ledging and perforations, but they do have an increasing tendency for breakage. They should be used only once to avoid problems. Some brands are the ProFile NiTi rotary instruments (Dentsply Tulsa Dental) including orifice shapers, ProFile 0.04 and 0.06 Tapers, Greater Taper (GT) files, and Accessory GT files, as well as the ProTaper instruments (Dentsply Maillefer, Tulsa, OK), which have 3 basic shaping instruments and 3 finishing instruments. The Quantec file (Analytic Endodontics, Orange, CA), which is a two-fluted instrument that increases file efficiency and reduces breakage, varies in taper and rate of taper to balance the file's strength with flexibility. Sonic and ultrasonic instruments were introduced in 1957 using electromagnetic ultrasonic energy. Piezoelectric ultrasonic units are also available. These units activate an oscillating sinusoidal wave in the file with a frequency around 30 kHz. The sonic devices at 2 to 3 kHz include the Sonic Air MM 1500, Megasonic 1400, and Endostar. The ultrasonic devices at 25 to 30 kHz include the ENAC, EMS PiezonMaster 400, Vetsonics Pet Piezo, and Piezo-Ultrasonic (all piezoelectric), and the CaviEndo (magnetostrictive). The piezoelectric unit has advantages over the magnetostrictive systems. Piezoelectric devices generate little heat; therefore, no cooling is needed in the electrical handpiece. The piezoelectric transducer transfers more energy to the file than the magnetostrictive system, making it more powerful. The magnetostrictive units require a watercooling and irrigation system. The ultrasonic devices use regular endodontic files (eg, K-files), and the sonic devices use special files known as Rispi Sonic, Shaper Sonic, Trio Sonic, and Heli Sonic.

Diagnosis of Endodontic Disease Endodontic treatment is required when the pulpal contents are undergoing an irreversible degenerative inflammatory process, or are necrotic and the tooth is needed as a functional part of the dentition. Death and necrosis of the pulp occur when it is invaded and overwhelmed by pathogenic bacteria and/or as a result of trauma. Many signs of the endodontically involved tooth may be observed at various times during the affected animal's distress. 13.36-44Localized facial edema or a fluctuant parulis or gum boil apical to the involved tooth would raise immediate suspicion of a dental abscess. Regional lymphadenopathy may be detected by palpation. Reduced biting pressure during play or aggression training may be noted, as may be reluctance to eat or refusal of food, especially hard or fibrous food, and the animal may even selectively eliminate harder items from its diet. To relieve discomfort during late signs of abscess development, the animal may constantly attempt to contact cool or cold surfaces and liquids. Fever may develop as the abscess reaches an acute stage. Clinical signs of teeth that require endodontic treatment have been outlined in various sources. 44-46 Teeth with periodontal disease may progress to induced endodontic disENDODONTIC INSTRUMENTS FOR ROOT CANAL

TABLE 1. Clinical Signs of Teeth Requiring Endodontic Treatment 1. Coronal fracture with bleeding. 2. Coronal fracture without bleeding; pulp canal can be probed with an endodontic explorer. 3. Crown is intact; tooth is discolored, showing pulpal necrosis (color may vary from red to black). 4. Soft-tissue signs: a. Fistulous tracts in muco-buccal fold over the root apex of the canine tooth. b. Infraorbital swelling from endodontically involved maxillary fourth premolar or first molar. c. Inframandibular fistula from draining canine tooth.

ease. 47,48 Clinical signs seen in fractured and intact teeth are shown in Table 1. Radiographically, the periapical abscess or granuloma may appear as a circular radiolucent area at the apex of the affected tooth; bony trabeculation is reduced or absent. 4z In the early stages of abscess formation, bony changes are not radiographically present. Because of this, periapical abscess cannot be eliminated from the differential diagnosis solely on the basis of a negative radiographic finding.

Pulpectomy Technique Pulpectomy involves removal of the contents of the pulp chamber and canal. There are 3 major goals of veterinary endodontic therapy that should be sequentially attained for reasonable assurance of success: 1. Initially, the entire contents of the pulp chamber and canal should be removed with endodontic files and irrigation. 2. Using endodontic files, the canals should be cleansed and enlarged so as to give the canal a slight funnel shape. 3. The apex (or apices) of the treated tooth should be sealed and the canal packed with an endodontic filling material. Antibiotic therapy is recommended in conjunction with endodontic therapy. There are many successful types of filling materials and methods in root canal therapy. A conceptual triad unifies the 3 aspects of sound endodontic treatment. These are access cavity design, canal preparation (or instrumentation), and filling (or obturation) of the root canal system.

Access Preparation To begin, any unsupported or fractured tooth structure should be removed to provide a clear view of the remaining sound tooth structure. At this point, the decision must be made regarding whether endodontic therapy can be effectively performed. There are AKC concerns when treating show dogs for which missing teeth is a disqualification. Every effort must be made to save these teeth to preserve the dog's show career. If the tooth is fractured to or below the level of alveolar bone, root canal therapy can still be employed. Coronal access sites have been described in detail. 49,5°-53 Coronal access is always made on the lingual surface of all anterior teeth. Access to the canine tooth is made on the rostral (mesial) aspect of the tooth. Access to the caudal teeth varies greatly according to the anatomy of each tooth. Often, the root canal is already exposed by tooth trauma. In any endodontic procedure, care should be taken to avoid bending the files as

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they are inserted into the canal. Access preparation should allow unimpeded straight delivery of the file to the apical canal. Radiography Dental radiographs are always an important part of endodontic therapy. The shape, length, width, and direction of the root canal are visualized on the radiograph. In multirooted teeth, the number and location of root canals, as well as the extent of curvature, is noted. The relationship between the endodontic system and the tooth structure is defined to help develop the relationship between the occlusal surface and the root canal. 52 All endodontic procedures begin with radiographs. Bur M a n i p u l a t i o n Penetration of dentin into the pulp chamber is always made with slow speed. The slowness of penetration enhances tactile sense, and the point at which the bur "drops" into the pulp chamber is more readily "felt." The fast cutting properties of a high-speed bur have been responsible for cutting into the facial wall or floor of the pulpal chamber, even when the drop into the pulp chamber had been detected. Therefore, the use of a slowspeed bur not only enhances tactile sense, but it also affords tactile control of the bur. The inadvertent cuts created by the use of high-speed burs are generally severe, even to the point of tooth perforation. Once access experience ts gained, high speed can be used. Similarly, once penetration into the roof of the pulp chamber has been accomplished, removal of the roof and all further bur manipulations within the pulp space must be performed with slow speed in a withdrawal motion, cutting from within the pulp space outward, to remove overhanging structure. This is best facilitated by using the bur (nonrotating) as an explorer and "feeling" the overhanging structure. This will aid you in detecting, by tactile sense, the overhanging ledges that are to be removed. With this knowledge, removal of the pulp chamber roof can be more safely achieved. Ideally, the pulp horn roofs should be included in the access. Make the initial penetration with a high-speed No. 2 round bur, preferably a diamond bur, to prevent shattering the tooth structure. The angle of penetration should be at right angles to the lingual surface of the crown. Use high speed to penetrate only the enamel, to the dentin, and to establish a preliminary outline form. Essentially, the preliminary outline form is an undersized cavity preparation established in the approximate shape of the final access preparation, and located conservatively within the outline of the eventual access cavity. This is the starting point from which the final outline will be achieved. Shape the preliminary outline form in a rounded and slightly elongated triangle with the base paralleling the incisal edge of the crown. Now switch to a slow-speed No. 2 or No. 4 round bur and alter the angle of the bur to a slightly more apical direction. Continue penetration into the dentin in this direction until the pulp chamber has been entered. If the radiograph indicates the pulp chamber is small or has receded, use a No. 2 round bur. Active hemorrhage may be present in teeth with viable pulp tissue. After penetration into the pulp chamber has been achieved, remove the overhanging roof structure of the chamber by cutting from within the chamber to the outside. Use a withdrawing, cutting motion toward the preliminary outline form. An explorer (DG-16) is used to detect the root canal and the direction of the canal.

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When the roof of the pulp chamber has been entirely removed, carefully insert the bur into the canal and, working from within the canal to the outside, remove the lingual shoulder. The intent is to establish an access from the root canal to the outline form that is continuous and smooth. Because of the variations in size and shape found in pulp chambers, the preliminary outline form should be smaller than what you should have envisioned as the completed outline form for that tooth. The mechanics of removing the pulp chamber roof will present a smooth continuous preparation with a straight-line access into the root canal. The access preparation of the coronal third of the tooth should be flared to allow direct access to the apical root canal. Gates-Glidden burs are used to flare the coronal access. They are capable of rapid dentin removal and must be used with care. Gates-Glidden burs are also susceptible to breakage and should not be forced into the canal. There are 6 sizes with a GatesGlidden #1 corresponding to a size 50 K-type file. They increase in 0.20-mm increments. Therefore, a #2 will be equal in size to a size 70 K-type file. One of the most common errors encountered in establishing access form in incisor teeth is the failure to remove the lingual shoulder. An unremoved lingual shoulder most often prevents straight-line access into the root canal and can cause ledging into the facial wall of the root canal, even to the point of perforation. Access form of the canine teeth is made in the exact center of the mesial or facial surface of the crown just coronal to the gingival margin.52,54.55 Location of the preliminary outline form is dictated by the height and position of the lateral incisor. The maxillary lateral incisor crown height may interfere with the straight-line access. Access form is always made on the occlusal surface of all posterior teeth. The mandibular first molar will have two roots. 56 The initial point of penetration to establish a preliminary outline form is in the exact center of the mesial groove and the exact center of the distal cusp. Make the initial penetration with a high-speed No. 2 or No. 4 bur. The penetration should be made in the exact center of these two sites. The radiograph will direct the position of the best approach. Penetrate the enamel and dentin and establish a preliminary outline form. Switch to slow speed and use a No. 2 or No. 4 round bur, and continuing in the long axis of the tooth, penetrate the dentin until the pulp chamber has been entered. When entering the pulp chamber of multirooted teeth, care must be taken to avoid cutting into and scarring the pulp chamber floor. Cutting into the pulp chamber floor may not only make it difficult to locate the orifices of the canals, but may also result in furcal perforation. You should not use a surgical length bur to penetrate into the pulp chamber. Do not allow the bur to drift laterally; severe scarring or perforation will occur. After you have penetrated the pulp chamber, remove the overhanging roof structure by cutting from within the chamber to the outside. The walls of the orifice of the root canal should be smooth, continuous, and slightly divergent. There are three roots in the maxillary fourth premolar. The initial point of penetration to establish preliminary outline form is centered over the distal root canal slightly distal to the distal developmental groove. The palatal (mesio-lingual) root is penetrated at the palatal pit, nearly over the furcation between the palatal and mesio-buccal root. The initial point of penetration to the mesio-buccal root is centered on this cusp one half KENNETH F. LYON

the distance between the cusp tip and the gingival margin. A transcoronal approach has also been described. 5r Three penetrations will be made using a high-speed No. 2 or No. 4 round bur. The angle of enamel penetration should be at right angles to the enamel surface. The distal outline form will be elliptical in shape. The palatal and mesio-buccal outline form will be round. Placing the bur too close to the palatal margin of the tooth can miss the palatal root canal. Switch to slow speed and using the No. 2 or No. 4 round bur, direct the bur toward the orifice of the distal canal, and penetrate the dentin until the pulp chamber has been entered. The pulp chamber is widest and longest in this direction to help avoid cutting and scarring the pulp chamber floor. To avoid furcal and floor penetration, do not use a surgical length bur to penetrate into the pulp chamber.

Canal Preparation: Debriding the Canal(s) When access preparation has been completed and the pulp chamber is exposed, the contents of the chamber, if any, are removed. A barbed broach is a tapered steel wire, round in cross~section, into which cuts have been made in the working end. 58 These cuts create barbs, which flare from the shaft of the wire in an outward direction. To use a broach properly, it must be inserted loosely into the canal, turned slightly to engage the pulp tissue, and withdrawn in the attempt to extirpate as much pulp as possible. Extreme care must be used in this procedure. The barbs are extremely fine and compressible. When a barbed broach is inserted into a canal to a point where it fits snugly, the slightest apical pressure can cause the barbs to be compressed by the canal walls, and the effort to remove the broach will embed the barbs into the canal walls like a fishhook. The attempt to withdraw the embedded barbed broach will predictably result in either barbs breaking off in canal walls or the broach itself breaking at the point of engagement. A broken barbed broach embedded in the canal wall is irretrievable. The HedstrOm file is a tapered steel wire, round in crosssecuon, whose flutes are cut in by a machine process. 58 As the name implies, it is a file, and thus the working action is on the withdrawal. It is a special type of file designed to be an aggressive and efficient instrument to remove dentin. However, because of its design, it is extremely susceptible to breakage particularly in the small sizes. After initial insertion of the file, usually a No. 15 or 20, the depth of insertion is marked by placing a rubber disk marker on the file. A radiograph is then taken, and the depth of the canal can be adjusted after correlation with the radiograph. This adjusted measurement will be the depth for all the files inserted when the tooth is treated. Hedstrom files should not be rotated. They are subject to fracture when rotated. Debris is cleaned from the file until it moves freely, and then the next larger file is inserted. The Reamer is a tapered steel wire, triangular in cross-section, which has been grasped at the very tip of the wire and twisted. 58 The twisting of the reamer during its manufacture produces the flutes in the instrument, thereby creating the working or cutting edges. Because of the angle of its flutes, the reamer can perform only one function: reaming. This reaming action is accomplished by placing the instrument in the canal to the first unforced contact, and then with slight apical pressure, the instrument is rotated no more than a quarter turn clockwise, and then withdrawn. It cuts, shaves, or reams the canal walls on insertion. The preparation, which results from a reamENDODONTIC INSTRUMENTS FOR ROOT CANAL

TABLE 2. Standardized Instrument Color Codes Color Code

Purple

White

Yellow

Red

Blue

Green

Black

Size

10

15 45 90

20 50 100

25 55 110

30 60 120

35 70 140

40 80

ing action, is more uniformly round than that produced by a file. The K-type file is a tapered steel wire, square or triangular in cross-section, which has been grasped at the very tip of the wire and twisted approximately twice as much as a reamer. 5s The action is to file or rasp, and this action is achieved on the withdrawal motion. Filing action is accomplished by placing the instrument into the canal to the desired working length, establishing pressure against the canal wall and, while maintaining this pressure, withdrawing the instrument without turning it. The angle of the file flutes is such that a cutting action is effected against the canal wall. The file need not contact all walls simultaneously to effect instrumentation to all surfaces. This file can also be used in a reaming action by placing it in the canal to the first unforced contact, rotating a quarter turn clockwise and then withdrawing. However, there is no apical pressure applied. Turning this file causes an engagement into the walls and pulls it deeper. Therefore, rotating no more than a quarter turn creates minimal engagement. Withdrawing the file then cuts away the engaged dentin walls. Standardized instruments (ISO sizes No. 10, No. 15, etc) are used. The instrument size is derived from the diameter at the working end, D1, which is measured in hundredths of a millimeter. The tip diameter is governed by a standard increase in diameter of 0.05 mm and does not have a constant percentage change between successive file sizes. 5s Additionally, a color code has been assigned for the various sizes (Table 2). The Profile Series 29 (Dentsply Tulsa Dental, Tulsa, OK) instruments are designed to have a constant 29% increase in size between each file and are not ISO-standardized. This creates more useful files at the smaller sizes, but can cause problems in the larger sizes, especially when the canals are curved. Greater Taper (GT) hand files (Dentsply Tulsa Dental) are active in a counterclockwise direction. The four GT files have a diameter of 0.20 mm and have increasing tapers of 0.06, 0.08, 0.10, and 0.12 mm/mm that correspond to fine, fine-medium, medium, and medium-large gutta percha master cones. The GT files are not ISO-standardized files. W o r k i n g Distance ( W o r k i n g Length) Working distance may be defined as that distance from the incisal edge, or some consistently identifiable reference point of the crown (eg, tip of a cusp on a posterior tooth), to a point 0.5 mm short of the radiographic apex. The apex of a tooth and the apical foramina are not synonymous. The apex is an anatomic landmark, and the apical foramina are located in an area, which may or may not coincide with the apex. Studies have demonstrated that, on average, the apical foramina are located approximately 0.5 mm short of the radiographic apex. Failure to accurately determine and maintain the working distance will result in either:

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1. Under extended instrumentation--failure to remove necrotic material; or 2. Overextended instrumentation--mechanically irritating the periapical tissue with the instruments, and creating an "open apex" through which debris, medicaments, and filling materials can extrude, causing additional insult to the periapex.59-61 Therefore, it is absolutely essential to establish the exact working distance before instrumentation is initiated, and to maintain this working distance throughout the entire cleaning and shaping procedure. The working distance is established and marked by placing a rubber endostop on the files. An examination of the diagnostic radiograph of the tooth is an aid in establishing the working distance and should: 1. Provide an approximate tooth length--this may not be a valid length, but a starting reference point. 2. Demonstrate the anatomy of the root canal system--can indicate size and shape of the pulp chamber and root canal. C o n d i t i o n s Requiring C u r v e d Files To establish a working distance in those roots that have known curves and those in which the apical third is difficult to visualize radiographically, it is wise to place a gentle curve in the tip of the file before insertion into the canal. Never force a file into a canal. This may result in ledging, perforation, or instrument breakage. Furthermore, it is not feasible to curve an instrument larger than a size No. 30. To produce a smooth, gentle curve m the apical third of the cutting portion of the file: 1. Grasp the file with the thumb and index finger of one hand where the cutting portion of the file begins. 2. Grasp the handle of the file with the thumb and index finger of the opposite hand. 3. With a slight bending pressure exerted on the shaft of the file, completely pull the file between those fingers holding the cutting position. The resulting curve will have been produced by intimidation rather than by an overt bending action. Using a hemostat should be avoided because this will produce too sharp a bend and can promote ledging, and may produce a weak spot where the file is grasped. Length-Determination Procedure 1. Using the radiograph of the tooth, measure the tooth from the incisal edge or cusp tip of the crown to the apex to obtain a radiographic tooth length. 2. Place a rubber stop on a No. 10 or No. 15 file to a distance 2.0 mm short of the measured radiographic tooth length to establish a trial distance. 3. Insert the prepared file into the tooth and passively advance it into the canal with a slight back-and-forth rotary or "wiggling" motion. Carefully advance this file as you explore the root canal. This rotary "exploring" motion should not exceed a quarter turn of the file. Continue until the rubber stop reaches the level of the coronal reference point of the tooth as explained in working distance. 4. In large canals, use a larger file than a No. 10. In small canals, use a No. 15 file. 5. With the file snugly in place to the full trial distance, take a radiograph. From this trial distance radiograph, you should be able to observe: 144

a. The relative distance between the radiographic tip of the file and the radiographic apex of the tooth. If the diagnostic radiograph and the trial distance radiograph are free from distortion, then the distance from the tip of the file to the apex should be 2.0 mm. b. The relative anatomy of the canal, including the existence of curves and the degree and the direction to which they curve. With this information, you will be able to safely adjust to the correct working distance without overextending instrumentation into the periapical tissues. 6. Adjust the rubber stop to allow placement of the file to a point 0.5 mm short of the apex. Radiographic confirmation will establish this distance as your working distance. The working distance should never be exceeded or shortened during the subsequent instrumentation of the apical portion of the root canal. Root canal debridement can be aided with the use of a chelating agent such as ethylenediaminetetraacetic acid (EDTA). Its function is three-fold: it helps debride the canal; it softens the dentin, making dentinal removal easier; and it lubricates the canal. As a dentin-softening agent, EDTA works very slowly. The EDTA is meant to chelate or remove metallic ions such as calcium by binding them chemically. The dentin-softening effect may be contraindicated in some cases, especially in small canals. Recapitulation Throughout the debriding or filing process, the root canal must be recapitulated. A smaller-diameter file is intermittently and finally inserted to the measured apical length, and the small bits of debris that are packed into the apex are removed to ensure total canal debridement. Recapitulation is a necessity for proper endodontic success. At this time, the canal is irrigated with a solution of sodium hypochlorite (household bleach). This is the irrigant of choice. It is able to lubricate, wash out debris, dissolve organic tissue, and destroys almost all of the microorganisms found in the root canal system. Do not force the irrigation so as to avoid penetrating the apical foramina. 59 Frequent irrigation of the canal to prevent the debris from becoming packed and possibly obstructing the canal is prudent. Two of the most important functions of this irrigant are to dissolve pulpal organic debris and to destroy all microorganisms in the root canal. 62 The principal reasons for using sodium hypochlorite as an irrigating solution are'. 1. to act as a lubricant for the file in the mechanical preparation of the canal; 2. to aid in the removal of instrumented material from the canal by floating it out (prevents dentinal shavings from packing in and occluding the apical region of the canal); 3. to aid, as an organic solvent, in the elimination of organic contents from the root canal spaces. 4. to act as a bactericide; 5. additionally, it can help to provide a bleaching action on those teeth that are discolored because of pulpal necrosis. Irrigation A root canal can be properly irrigated by correctly using the following procedure: 1. Place the irrigating syringe needle loosely into the canal. KENNETH F. LYON

2. Apply passive pressure to the syringe plunger to gently express the solution. If there is any doubt that the solution is not filling the entire canal, tease the solution to the entire working distance with a file. 3. Suction off the excess. 4. Keep the tooth filled and constantly refreshed with the solution during instrumentation. 5. Never place a suction tip into a canal to where it binds. A reverse pressure on the periapical tissue could conceivably be as damaging as a positive pressure. 6. Forced irrigation results in the irrigating solution being expressed through the apical foramina into the periapical area. This also forces debris and bacteria from the canal into the periapical tissue. Sodium hypochlorite in contact with vital periapical tissue can cause a severe pain reaction and swelling. The bleach should be irrigated from the canal with a final saline irrigation. When the canal(s) have been irrigated for the final time, residual moisture must be eliminated before the canal can be filled. This can be performed by repeatedly inserting individual absorbent paper points into the canal. Successful endodontic therapy is best attained with a dry canal before the final filling procedure.

Conventional Root Canal Technique The mechanical objectives for root canal preparation include: maintaining the instrumentation within the root canal; and maintaining the original shape of the root canal; creating a tapered funnel preparation and a solid apical stop. A standardized or conventional technique is an attempt to shape the canal to the same size, taper, and configuration of standardized instruments. The most common flaring technique is termed the "step-back." Root canals will have variable characteristics with respect to curvature, taper, length, width, and the presence of obstructions in the canal. Canal Preparation 1. Once coronal access is completed, use a barbed broach to carefully extirpate the contents, or as much of the contents as possible, of the radicular portion of the root canal. 2. Length-determination procedure: Make a diagnostic radiograph of the tooth selected for root canal instrumentation. Determine the trial distance length, and make a radiograph with the trial file in place. 3. Establish the working distance and make a radiograph of the tooth with the file in place to the working distance. The instrumentation technique is called a chemomechanical preparation, which includes irrigation. Using this technique requires that you keep the canal filled with the irrigating solution during the entire instrumentation phase. Sodium hypochlorite is an organic solvent and will greatly aid in the dissolution and removal of organic contents from the pulp spaces (vital or necrotic pulp tissue that escaped barbed broach debridement, exudates, hemorrhage) and must be constantly refreshed and renewed to effect its maximal working properties 4. With the initial file in place to the exact working distance, rotate the file clockwise no more than a quarter turn, and then slightly withdraw 2 to 3 mm. Because the initial file is loose, care must be taken not to exceed the working distance (as indicated by the rubber stop). This is less of a danger as larger files are used, because as the diameter of the canal is enlarged at ENDODONTIC INSTRUMENTS FOR ROOT CANAL

the working distance (within the tooth structure), a definite apical stop is created that can be tactically sensed. After three or four manipulations, remove the file and wipe it clean with a gauze sponge. This is repeated until the file can be placed to the working distance without any resistance. 5. Proceed to the next larger file. Do not skip sizes. Place the rubber stop to the working distance and gently insert the file to the first unforced contact by the canal walls. This will usually occur somewhat short of the working distance. As contact with the canal walls becomes more definite, it will become necessary to completely withdraw the file after each quarter turn and wipe its flutes clean. The principle of a quarter turn clockwise is employed until the full working distance has been achieved. Instrumentation for that file is complete when it can be inserted to the full working distance and withdrawn without any resistance. 6. This procedure is repeated again and again until the apical third of the canal has been cleaned and shaped. Rapid increases in file size may become apparent when a large canal is instrumented. This is best determined by the presence of clean dentinal shavings on the file. When you detect these shavings, then instrument the canal one size larger. At this point, the apical third of the canal can be considered fully "instrumented." Record this file size. 7. The coronal portion will now be instrumented using a filing motion. Select as large a file as possible that is still loosefitting in the coronal two thirds of the canal. Place a rubber stop on the file 5.0 mm short of the working distance. Place the file in the root canal to this new length and file the canal by withdrawing. Working circumferentially around the canal, this creates a slightly larger taper than that prepared in the apical third. Remember to keep the canal filled with irrigating solution. Peeso reamers can be used to flare the coronal third of the canal. Your preparation should now be a canal that has been cleaned and shaped throughout the length of the working distance. The apical termination of the preparation should be within tooth structure. The apical third of the preparation should reflect the size and taper of the last file used. The instrument filing motion should have completed the coronal two thirds of the preparation. This greater flare will not interfere with the master cone that will seat and fit snugly in the apical third. Also, the coronal flare facilitates lateral condensation. 8. Place your last file used to instrument the canal to its full working distance and make a radiograph. Irrigate the canal with the sodium hypochlorite, followed by saline, one last time and dry the canal with sterile paper points. You are now ready for obturation of the root canal.

Filling the Canal(s) The goal of complete root canal treatment is the total threedimensional obturation of the prepared root canal and pulp spaces. The foramina at the apex of the tooth are not the sole communication of the pulp spaces to the external surface of the root. Dentinal tubules on a microscopic scale, as well as accessory and lateral canals on a macroscopic scale, can and do communicate with the external surface of the root. It is therefore a requirement to seal the root canal throughout its preparation as at the apical foramina. This will prevent microorganisms from entering and reinfecting the tooth by percolation. Achieving an apical and coronal seal of the root canal is most important.

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Obturation of the endodontic system is accomplished by many techniques. 63 These techniques include master cone or primary cone, lateral condensation, vertical condensation, lateral-vertical condensation, thermocompaction, injection (thermoplasticized), and solvent (chloropercha and eucapercha) techniques.64, 65 Obturation or the filling of the root canal is the culmination of the procedure in root canal therapy. The entire regimen of treatment to this point has been to establish the tooth in a biologically compatible status, and to shape and facilitate filling the canal. Failure to fully obturate and seal the canal will lead to endodontic failure. Therefore, the selection of a proper root canal filling material is a critical phase in achieving the objectives of root canal therapy. No single material yet fulfills the ideal requirements. However, a combination of materials comes close to the ideal and affords an adequate root-canal filling material: gutta percha and root canal sealer. Gutta Percha Gutta percha is a purified, coagulated milky exudate of certain trees found in the Malayan Archipelago. It is closely related to rubber. In fact, it is the trans-isomer of the rubber polyisoprene radical. It is to this substance that the manufacturers add additional ingredients and supply them to the endodontic world as gutta percha cones. The gutta percha is selected to correspond to a filed diameter root canal (ie, a size 40 gutta percha point to fill a root canal filed to a size 40). When placing the gutta percha, the master cone is selected and is inserted slowly into the canal to allow air and excess sealer to escape around the cone. The master cone size corresponds to the last file used when instrumenting the canal. Then, a spreader is used by placing it into the canal between the master cone and the canal wall. Lateral condensation is used to place pressure in an apical direction. The taper of the spreader is the mechanical force that laterally compresses and spreads the gutta percha. The spreader is creating the space for an additional accessory cone, which will then be placed within the canal.

and Apexit (Vivadent, Schaan, Liechtenstein), polymers such as Endofill (Lee Pharmaceuticals, South E1 Monte, CA), AH Plus (Caulk/Dentsply, Milford, DE), and Diaket (ESPE, Seefeld, Germany), glass ionomer cements such as Ketac-Endo (ESPE); and formaldehyde-containing sealers (which can be very toxic) including Kri paste, Endomethasone, Riebler's paste, and N2. Several sealers and cements, such as AH26, AH Plus, KetacEndo, and Diaket, may be used as a sole filling material in small-diameter canals, because they have sufficient volume stability to maintain a seal. In cement tests, some showed marked inflammation of the apical connective tissue, coupled with edema and, in some cases, necrosis with all material tested except zinc oxide and eugenol. 6r-r2 Zinc oxide and eugenol appears to demonstrate the properties most desirable for canine and feline endodontics. Sealers are used to create and maintain an apical seal. The root-canal cement or sealer is placed by using Lentulo spiral fillers on a reduction gear contra-angle, or by using the endodontic files, and injection techniques are also described. The Lentulo spiral drills are coated with paste, and the drill is spun into the canal so that the spirals are carrying the paste deep into the canal. These filling techniques may be difficult to control, and care must be taken to avoid overfills. Sealer is added to the canal with a filler spun clockwise. Lateral C o n d e n s a t i o n O b t u r a t i o n T e c h n i q u e 1. Select a gutta percha cone that is the same size as the last file used in cleaning and shaping the canal. For example, if a No. 60 file was the last file you used to prepare the canal, a No. 60 gutta percha master cone should be selected. Grasp the cone with Cotton self-locking pliers at a distance 0.5 mm less than the recorded working length, and place it gently, but firmly, into the canal. The cone must not be bent or buckled during this procedure. The cone must meet the following two criteria before making a ra&ograph for "confirmation-of-fit."

Root Canal Sealers

a. It should extend into the prepared canal to a distance 0.5 mm shy of working length. b. It should fit tightly enough to resist withdrawal from the canal (tug-back).

Gutta percha alone is not capable of sealing a root canal. Even in the most precise adaptation to the prepared canal, microscopic spaces will exist and allow leakage. To achieve an adequate seal, root canal sealers are used in conjunction with gutta percha to provide that measure of total obturation. An appropriate root canal cement or sealer is selected to be: (1) bactericidal; (2) completely compatible with the periapical tissues; and (3) adhering closely to the walls of the root canal and the root canal filling material, thereby serving to bind them together. Most of these come as a powder and liquid spatulated together to a thickened consistency and then introduced into the prepared root canal. Zinc oxide/eugenol cements include Rickert's sealer (Kerr, Romulus, MI), Proco-Sol (Star Dental, Conshohocken, PA), U/P-Grossman's sealer (Sultan Chemists, Englewood, NJ), Wach's sealer (Sultan Chemists), Tubli-Seal (Kerr), Endomethasone (Septodont, Saint-Maur, France), and N2 (Agsa, Locarno, Switzerland) and basic zinc oxide with eugenol. 66 Others include Kloroperka N-f) (N-O Therapeutics, Oslo, Norway), a chloropercha-type sealer, calcium hydroxide sealers such as Sealapex (Kerr), CRCS (Hygienic Corp, Akron, OH),

Silver cones, which were introduced in 1930, are no longer considered an adequate filling material. Originally, a commonly used test of "tug back" was to see if the patient's head could be raised from the headrest by pulling on the silver point, r3 2. When the two criteria are satisfied, make radiographs to verify the cone working-distance relationship. These radiographs should show both the proximal view as well as the facial view. If the diameter of the cone is too large, it will stop appreciably short of the prepared working distance. If the diameter of the cone is too small, it will be loose in the canal or pushed beyond the working distance, and it will extend through the foramina or bend back upon itself. The proper cone will fit the prepared canal snugly in the apical fourth to a distance 0.5 mm shy of the working length. The pressures exerted upon the gutta percha during lateral and vertical condensation will cause the gutta percha to be compacted into the remaining 0.5 mm, thereby obturatmg the canal to the prepared apical seat. Select the proper size root canal plugger to be used at this time. Select the largest plugger that can be loosely inserted into the canal at least half the length of the root. Make your selection now, because once root canal filling material has been placed

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into the canal, the opportunity to select the proper plugger no longer exists. 3. Mixing the sealer When used alone, gutta percha cannot hermetically seal a canal. No matter how tightly fitted, adapted, or compacted; many studies have shown that leakage will always occur. The purpose of the sealer, then, is to provide the last measure of obturation that will achieve a total seal. There are many sealers on the market, which contain varied ingredients. Zinc oxide and eugenol is the most commonly used nonstaining sealer used in veterinary dentistry. All sealers require that they be mixed to a creamy consistency to the point at which the mixture will cling to the spatula for a distance of 3/4 to 1 inch as it is withdrawn from the glass slab. a. Place a small amount of zinc oxide root canal sealer powder about the size of a quarter at one end of a clean, dry glass slab, and place three drops of eugenol in the center of the slab. b. With a #5 spatula, incrementally incorporate a small amount of powder into the liquid (eugenol) and mix in a circular motion until the mixture is smooth and creamy. Unless the mixture is well spatulated, the ingredients of the powder will impart a granular texture to the mixture. Such a granular consistency would prevent proper seating of the preselected master cone. c. Apply the proper mix test. Place the spatula tip into the pool of mixed sealer and then slowly raise the spatula away from the glass slab. The mixing procedure should take about 2 minutes. 4. Place the sealer into the prepared root canal using a Lentulo spiral filler on a 10:1 reduction gear contra angle on a low-speed handpiece. Coat the spiral filler with sealer and insert into the root canal and rotate clockwise to deposit the sealer on the canal walls. Do not use an excessive amount of sealer; the intent is to lightly coat or condition the walls, and not to fill or place excess sealer into the canal. A file coated with sealer can also be used in a counterclockwise fashion to deposit the sealer. In large canals, a paper point can be used to coat the canal walls. 5. Coat the master cone evenly with sealer and replace it in the same position it occupied when verified by the radiograph. In placing the master cone into the canal, there must not be excess sealer extending beyond the apical tip of the cone. Placement of the cone should be slow and steady. Any slight withdrawal and reentry may effect a pumping action and result in excess sealer between the cone tip and the apical foramina. Pressures from cone placement and lateral and vertical condensation may force this excess material beyond the foramina and into the periapmal spaces. It must be emphasized that the desired and expected healing following root canal therapy is complete closure of the apical foramina with cementum. Overextended root canal filling material will prevent such healing. Although the sealer is absorbable in time, it is a constant source of periapical inflammation. 6. After the master cone has been seated, ad&tional gutta percha cones are placed in the canal by the lateral condensation technique. The root canal spreader is fitted with a rubber stop 3 mm shy of the working distance. Space for the accessory cone is provided by inserting the spreader into the canal alongside the master cone under controlled slight pressure. This slight pressure is exerted vertically in the long axis of the tooth, forcing the gutta percha against the canal walls. Several back-and-forth rotations of the spreader, while slight apical pressure is applied, ENDODONTIC INSTRUMENTS FOR ROOT CANAL

will aid in creating the necessary space for the accessory cones. The depth to which the spreader is inserted into the canal is dependent on the size and shape of the cervical two thirds of the root. Under no circumstances should the instrument be inserted beyond the measured length indicated by the rubber stop. The shape of the space created is the shape of the root canal spreader. Gently withdraw the spreader from the root canal using a back-and-forth rotating movement and immediately insert a prepared accessory cone into the newly shaped space. This is necessary because gutta percha will rebound after the spreader is removed. The accessory cone should be slightly smaller than the spreader. Remove the spreader and immediately insert the accessory cone. Repeat this procedure of laterally condensing the gutta percha and adding accessory cones again and again until the canal has been fully filled to the cervical line. The last insertion into the canal is an accessory cone. Although this procedure is one of lateral condensation, the mechanics are such that a vertical pressure is also imparted. It is this vertical pressure that causes the apical 0.5 mm of the prepared canal to be filled. 7. A heat-transfer instrument is used to transfer heat to the gutta percha. The heated plugger/spreader is most often used. Vertically condense the cervical portion of the warm gutta percha using the plugger. Sear off the excess gutta percha with a hot instrument (a Glick #1 or a heater-plugger. A Glick #1 was developed specifically for removal of excess gutta percha with the heater/plugger end.) A hot excavator may also be used. The gutta percha can also be laterally condensed using the Touch ~n Heat or System B (Analytic Technology, Orange, CA). The spring-controlled handpiece will heat up the tip of the Touch 'n Heat as it is placed into the filled root canal and removed quickly, so as not to remove the gutta percha filling. After lateral condensation, the Touch 'n Heat can then be used for cutting off the gutta percha cones from the crown down to a level 2 mm apical to the cervical line. 8. When the gutta percha cones have been cut off, take the preselected root-canal plugger and apply apical pressure to the total mass of gutta percha for vertical condensation. The plugger should be slightly smaller than the root canal so that pressure exerted will be solely on the gutta percha, and not on the tooth structure. This final vertical pressure is to complete the compaction of the gutta percha within the body of the root and create a dense three-dimensional obturation. 9. Make a radiograph to demonstrate the completeness or incompleteness of the root canal filling. If the canal is not completely obturated, the gutta percha will need to be removed and the procedure started over again. 10. The coronal chamber must be thoroughly cleaned. All sealer and gutta percha fragments must be removed. Clean excess sealer using alcohol soaked cotton pellets.

Access Restoration Following filling of the canal, a restoration can be placed after an undercut is created by using an inverted cone bur. r
restorative. An undercut cavity preparation is completed before placement. A glass ionomer is mixed, placed, and allowed to cure (or light-cured if a VLC product is used). After curing, the glass ionomer is undercut with an inverted cone bur. The enamel is acid-etched and rinsed well. A bonding agent is applied and cured before placement of a light-cured composite restorative material. The composite is finished and polished. If a self-cure or auto-cured composite is chosen, they require mixing the bonding agent with the composite, and then placing the composite in the undercut cavity preparation. This is followed by compressing with a composite instrument or plastic mamx. The composite is then finished and polished.

Evaluation of Obturation Radiographic evaluation is the only immediate method of assessment of the obturation. Study the obturation radiograph for radiolucencies indicating voids or incomplete obturation. The filling material should be of uniform density from apical to coronal aspects, with sharp and distinct margins. 77 The material should extend to the working length and should reflect the shape of the canal, tapering from coronal to apical. Further evaluations should be scheduled at 2 weeks and 6 weeks, followed by radiographs at 6 months, and then yearly radiographs.

control moderate pain. Opioids, such as butorphanol, act centrally and when given orally, manage moderate to severe postoperative pain.

What and When to Refer A board-certified veterinary dental specialist, a Diplomate of the American Veterinary Dental College, may be available for referrals. The veterinarian should be very selective in the chmce of cases to treat, knowing that it may be stressful as well as time-consuming to resolve any endodontically comprised tooth. Our clients are generally well informed m treatment of dental problems and may request a higher level of expertise to treat their pet's dental problems. Difficult cases should be referred to a specialist. Those cases presenting with an unusual degree of technical difficulty should also be referred. Clients should be informed that treatment procedures would be timeconsuming and more expensive. Ultimately, the knowledge that advanced endodontic procedures are available and are frequently completed in dogs and cats allows veterinarians to save teeth that may have been lost to extraction or serious dental refections.

Summary Crown Restoration Some clients will choose to have the crown restored with a cast crown on an endodontically treated tooth. Full cast crowns may be placed, as well as direct-bonded composite restorations. The full metal crown will give the best protection to the endodontically treated tooth. The type of crown requested is often a financial decision, and choice of materials can cause the cost to vary (ie, titanium vs gold). Most cast crowns are fabricated by human dental laboratory services, but veterinary dental laboratories are available.

Antibiotics and Analgesics Numerous bacteriologic studies on endodontic infections show that the predominant microorganisms are facultative and obligate anaerobes. Guidelines for use of antibiotics in veterinary endodontic patients have not been established. The rational use of antibiotics is based on several factors: the proper indication, the effectiveness of the drug against the invading organism, and the toxicity of the drug to the patient. Prophylactic antibiotic regimens are indicated for cardiac patients and patients with systemic disease conditions. Many endodontic infections respond rapidly to root canal therapy and do not require systemic medication. If the antibacterial spectrum were the only criterion, clindamycin would be the drug of choice for treating endodontic infections. It is especially effective against Bacteroides sp and periapical mfections. Penicillins are nearly as effective against oral strains of Bacteroides sp and may be more effective against the gram-positive organisms. Oral analgesics effectively control postoperative endodontic pare. Clinical pain can be associated with inadequate canal preparation, iatrogenic perforations, overinstrumentation and periapical inflammation. Periradicular pain occurs more often in the veterinary patient. If the patient is suffering with pain, then an analgesic is recommended. Nonsteroidal anti-inflammatory drugs, such as aspirin and carprofen, act peripherally to

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As more veterinary patients present for treatment of endodontic dtsease, it becomes more evident that veterinary dental practitioners must become proficient in a variety of different endodontic techniques. Studies have show the effects of endodontic disease and the effects of treatment of the root canal system. 78,79In the rapidly progressing field of endodontics, it is also important for veterinarians to continue their training and expand their knowledge of instrumentation, materials, and techniques. Veterinary clients have an increased awareness of dental health and do not choose to have endodontically compromised teeth extracted. More and more root canal procedures are being performed with predictably successful results, s° The modern era of veterinary endodontics has arrived, and most of this current information comes from human dental textbooks. 8~ Familiarity with techniques covered in this article and with advances in veterinary endodontics will become necessary. The future appears to be very promising when we are equipped with the increased understanding and the technological skills of modern veterinary endodontics.

References 1. Lyon KF. Endodontic therapy in the veterinary patient. Vet Clin North Am Small Anita Pract 28:1203-1236, 1998 2. Fiorito DA. Endodonhcs. In Proceedings of the 2nd Annual Meeting of the Academy of Veterinary Dentistry, New Orleans, I_A, 1988, pp 6-7 3. Frost P. Standard root canal therapy. In Proceedings of the 11th Annual Veterinary Dental Forum, Denver, CO, 1997, pp 64-68 4. Goldstein GS. Endodontic therapy: methods and materials of routine endodontics. In Proceedings of the 4th World Veterinary Dental Congress, Vancouver, Canada, 1995, pp 36-38 5. Goldstein GS, Anthony JMG. Basic veterinary endodontics. Compend Contin Educ Pract Vet 12:207-217, 1990 6. Gorrel C, Robinson J. Endodontics in small carnivores, In Crossley DA, Penman S, (eds): Manual of Small Animal Dentistry, ed 2. United Kingdom, BSAVA, 1995, pp 168-181 7. Harvey CE. Endodontics, In Proceedings of a Course in Small Animal Dentistry and Oral Surgery. Publication No. 136, Veterinary ContinuKENNETH F. LYON

8. 9. 10. 11. 12.

13.

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22. 23.

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28.

29,

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