Mark M. Smith, VMD, DACVS, DAVDC
Exodontics is the practice of tooth extraction. The most common indication for exodontic therapy in dogs is severe periodontal disease. Endodontic therapy is recommended for teeth affected by crown fracture exposing pulp, and pulpitis. However, it is not unusual to perform exodontic therapy when there is minimal crown available for restorative techniques, or when the owner does not authorize endodontic therapy. Exodontic therapy may also be used as a component of treatment for malocclusion.
The periodontal ligament attaches the tooth to the bony alveolus or socket. The goal of exodontic therapy is to disrupt the periodontal ligament allowing movement of the tooth out of the alveolus. This component of the exodontic process is performed with periodontal elevators. There are various sizes and grip configurations for periodontal elevators. In dogs, basic periodontal elevators include instrument numbers 301s, 301, and 401.
After the gingival attachment fibers are severed with a small scalpel blade, the periodontal elevator is inserted into the potential space between the tooth and alveolar bone. Initially, the elevator is rotated in the periodontal space to fatigue and tear the periodontal ligament. The position of the rotated periodontal elevator is maintained for 10 seconds to accomplish this goal. This maneuver is performed around the circumference of the coronal aspect of the root. As the exodontic procedure continues apically, the blade of the periodontal elevator is placed parallel to the root surface; the handle is dropped to be perpendicular to the long axis of the root; and the blade is turned 90 degrees. This allows the edge of the elevator to engage the side of the root and "elevate" the root from the alveolus. Again, after movement is maximized, the position of the periodontal elevator is maintained for 10 seconds. Progress during the exodontic procedure will be noted by increased movement of the root and crown as the periodontal space expands secondary to hemorrhage and disruption of the periodontal ligament. Controlled force and patience will allow most single-rooted teeth or tooth segments to be extracted with periodontal elevators and digital manipulation. Extraction forceps are used only after the tooth is so mobile that the clinician considers the tooth or tooth segment removable with digital manipulation. The extraction forceps should engage the tooth as far apically as possible in order to decrease leverage forces on the root which could lead to root fragmentation.
Generally, these non-surgical techniques are effective for incisors, first premolars, and third molars regardless of the health status of the periodontium. Multi-rooted teeth with periodontal disease and secondary mobility may be extracted using similar techniques.
Non-mobile, multi-rooted or canine teeth are considered difficult or complicated teeth to extract. This fact is based on the size or complexity of the root system and sufficient periodontal attachment to prevent mobility even when there is substantial periodontal disease. Periodontal disease-free teeth with endodontic disease or malocclusion may be particularly difficult to extract based on having normal periodontal attachment. Surgical techniques are usually required for exodontic therapy of these teeth. Principles for surgical exodontic therapy include periodontal flap elevation, removal of alveolar bone to partially expose the root(s), sectioning of the crown in multi-rooted teeth, crown/root segment elevation, alveoloplasty to smooth rough bone edges, and suturing of the periodontal flap over the alveolus. These principles will be highlighted in the following paragraphs describing surgical exodontic techniques for the maxillary fourth premolar, mandibular first molar, maxillary canine, and mandibular canine teeth.
Maxillary Fourth Premolar
The maxillary fourth premolar is a trirooted tooth with a large distal root and 2 mesial roots (mesiobuccal and mesiopalatal) emanating from a common root trunk. The procedure begins by using a # 15 scalpel blade to incise a mucogingival periodontal flap. The mesial and distal incisions are made along the line angles of the tooth. Care should be taken to avoid the gingiva at the distal aspect of the maxillary third premolar and the mesial aspect of the maxillary first molar. Dorsal length of the incisions are dependent upon the size of the tooth, usually extending between 1.5 and 2.5 cm. As the mesial incision is advanced dorsally, another area to avoid is the infraorbital foramen which can be palpated through the mucosa between the maxillary third and fourth premolars. The infraorbital artery and nerve exit this foramen as they course in a rostral direction. After these vertical incisions are made, gingival fibers are incised from their attachment using either a # 15 scalpel blade or a small, sharp periosteal elevator. The gingiva is thin and easy to perforate when using a sharp instrument. The technique of placing the scalpel blade parallel to the tooth surface and below the gingiva, followed by short stab and prying motions is an effective way to elevate this tissue. As the mucogingival line is approached, a sharp periosteal elevator is used to elevate the buccal mucoperiosteum completing the flap.
Alveolar bone is removed from the buccal aspect of the distal and mesiobuccal roots using a high-speed handpiece and a round or pear-shaped bur. Usually the coronal one half to two-thirds of the root is exposed by using light hand pressure to bur away this thin bone. During the alveolectomy process, it is helpful to drill slots on the mesial and distal aspects of these roots. Such bony slots provide a location to place the periodontal elevator. An analogy for this maneuver might be a toe-hold during mountain climbing. During the alveolectomy, developing these "toe-holds" for the periodontal elevator will speed the extraction process. If a high-speed handpiece is not available, other instrumentation may be used for alveolectomy including bone file, rongeurs, curette, or a hobby drill with a sterilized round bur.
Crown sectioning is performed using a tapered-fissure or crosscut bur. The critical landmarks for crown sectioning are the buccal and mesial furcation entrances. Using these landmarks ensures crown sectioning with one root per crown segment. An exact "hemisection" is not necessary, however the crown must be completely cut beginning at the furcation entrances indicated. If a high-speed handpiece is not available, other instrumentation may be used for crown sectioning including a hobby drill, hack saw, or large bone cutter. This latter instrument will likely shatter the crown however crown integrity is not an important factor; only separation of the crown at the furcation.
The crown/root segments are elevated and removed using simple exodontic techniques described previously. Since the buccal alveolar bone has been removed, the crown/ root segments are not elevated as much as luxated in a buccal direction. Therefore, this maneuver is easier with removal of increased amounts of buccal alveolar bone.
Following removal of the crown/root segments and confirmation that the roots have been completely removed, sharp bony edges are reduced (alveoloplasty) using a high-speed handpiece and a round or pear-shaped bur. Other instruments may be used for alveoloplasty as described for alveolectomy. Alveoloplasty minimizes perforation of the periodontal flap by sharp bony edges. It also removes edges of bone which would quite likely require resorption during osseous healing.
Dilute chlorhexidine (0.12%) may be used to lavage the wound followed by positioning of the periodontal flap over the extraction site. The flap is sutured to the buccal mucosa and mucoperiosteum of the hard palate using chromic gut or polyglactin 910 in a simple interrupted pattern. Polydioxanone is not recommended because of its prolonged resorption time which is not necessary for routine oral wounds. Space is provided between individual sutures so that drainage may occur from the extraction site.
Mandibular First Molar
Similar exodontic techniques are used for the mandibular first molar as the maxillary fourth premolar. The periodontal flap, lateral alveolectomy, and alveoloplasty are performed as described previously. It should be noted that when compared with alveolectomy of the maxillary fourth premolar, the thickness of bone on the buccal aspect of the mandibular first molar is substantially greater. Crown sectioning is also recommended for this tooth with the shortest path being through the crown from the furcation in a distal direction. Lateral alveolectomy, visualization of the mesial and distal roots, and controlled root elevation decrease the incidence of iatrogenic mandibular fracture.
The maxillary canine is a large, single-rooted tooth which is difficult to extract using non-surgical techniques. Canine teeth affected by severe periodontal disease may be extracted using non-surgical methods, however if the tooth has a healthy periodontium, it is essential to implore surgical exodontic techniques. It is important to note that the root of the maxillary canine courses in a dorsal and distal direction with its apex directly above the mesial root of the maxillary second premolar. The periodontal flap incision begins in the buccal mucosa over the maxillary second premolar and is directed mesially, sloping towards the gingiva at the distal line angle of the canine tooth. The gingival attachment fibers are incised along the canine tooth in a manner described previously. The flap incision is completed with a vertical relief incision from the gingiva along the mesial line angle approximately 3/4 the length of the canine tooth root. Following gingival elevation, the buccal mucosa is relatively easy to mobilize from the buccal alveolar bone.
An alternate flap design includes a peninsula-shape flap with mesial and distal incisions over the tooth's line angles. Generally, regardless of flap design, the flap is sutured over bone. Therefore, the alveolectomy should be offset when compared with the periodontal flap. Lateral alveolectomy is performed using methods described previously. The alveolectomy begins near the cementoenamel junction and continues apically along the canine root. The cementum has a tan color and is readily identified compared with the hemorrhagic alveolar bone on the mesial and distal sides of the tooth.
During the alveolectomy process, it is helpful to purposely make gauges or slots in the alveolar bone on both the mesial and distal aspects. These focal areas of bone loss provide locations for application of the periodontal elevator. The canine root is elevated with the tooth being displaced in a lateral or buccal direction. If the angle of buccal displacement is acute, the root apex may fracture through the thin alveolar plate of bone separating the alveolus from the nasal cavity. If fracture leading to perforation occurs, hemorrhage may be noted from the ipsilateral nares. This problem is treated by primary wound closure of the periodontal flap over the alveolus. Incising the periosteum at the base of the periodontal flap improves flap mobility and decreases wound tension during primary closure.
A buccal (lateral) approach has been recommended for surgical extraction of the mandibular canine tooth. This approach requires consideration of anatomic structures including the prominent soft tissue attachment (frenulum) of the lip, the neurovascular structures exiting the mental foramen, and the roots of the first and second premolar. Considering the orientation of the root of the mandibular canine tooth is in a lingual (medial) direction, it would seem appropriate to consider an approach that could be performed directly over the root. Such an approach would avoid disruption of lip frenulum, potential hemorrhage from the mandibular artery and vein at the mental foramen, and iatrogenic trauma to adjacent tooth roots. A lingual approach for surgical extraction of the mandibular canine tooth has been developed based on anatomic observations of tissues and structures of the rostral mandible and lingual orientation of the mandibular canine tooth root.
The initial component of the procedure is elevation of a lingually based, full-thickness, mucoperiosteal flap. The flap is based on the symphyseal surface near the mandibular symphysis. The flap apex includes the gingiva of the lingual aspect of the mandibular canine tooth. Generally, the flap base is approximately twice the width of the flap apex. A nitrogen powered dental unit with a high-speed handpiece and round bur are used to perform lingual alveolectomy. Length of alveolectomy ranges from 10-20 mm in dogs. Periodontal elevators and extraction forceps are used to complete the extraction. The remaining alveolus is lavaged with 0.12% chlorhexidine and the flap is apposed to the buccal gingiva using 3-0 polyglactin 910 in a simple interrupted pattern.