Case Report Self-Inflicted Lingual Trauma Secondary to Inferior Alveolar Nerve Block in 3 Horses F

EQUINE VETERINARY EDUCATION / AE / MARCH 2012 119

Case Report Self-inflicted lingual trauma secondary to inferior alveolar nerve block in 3 horses F. J. Caldwell* and K. J. Easley† Department of Clinical Sciences, College of Veterinary Medicine, Auburn University, Alabama, USA; and †Equine Veterinary Practice LLC, Shelbyville, Kentucky, USA.

Keywords: horse; equine; lingual trauma; mandible; regional anaesthesia; nerve block

Summary with the technique, exodontias are being performed more frequently via oral extraction with the horse standing. Oral Exodontia is the typical treatment recommended in severe extraction is technically easier to perform in the conscious cases of dental disease where alternative treatment patient and additionally avoids the risks and expense techniques fail to salvage the affected tooth. Exodontias associated with general anaesthesia. The utilisation of local are frequently performed in the standing horse with the anaesthesia for these procedures greatly enhances the benefit of sedation and regional anaesthesia in order to overall comfort of the horse and ease of surgery. Techniques avoid the risks and expense of general anaesthesia. The for local anaesthesia of the oral cavity in the horse inferior alveolar nerve block is commonly utilised when have been well described in the literature (Fletcher extracting diseased mandibular dentition. Because of the 2004; Schumacher 2006; Tremaine 2007; Doherty and close anatomical relationship of the lingual and inferior Schumacher 2010). alveolar nerves both may be desensitised following To perform surgery in the conscious patient, adequate anaesthesia of the inferior alveolar nerve. Desensitisation of analgesia is necessary for proper restraint and control of the tongue may result in horses traumatising it during the animal. Although many types of local anaesthetic mastication before sensation returns. This report describes agents are available, only a few such as lidocaine, 3 horses that sustained self-inflicted lingual trauma mepivicaine and bupivicaine are commonly used in the following inferior alveolar nerve blocks performed for horse. These drugs are relatively nonreactive and do not standing oral surgical procedures. cause significant localised reaction when injected cutaneously or submucosally. Side effects of nerve blocks Introduction of the head in horses include haematoma formation from arteriopuncture, orbital prolapse, Horner’s syndrome, Dental disease is the most frequent anomaly of the equine neuropraxia, cellulitis and temporary lip paralysis (Tremaine oral cavity and, in severe cases, may require oral surgical 2007; Dixon et al. 2009). Reports of complications procedures for resolution (Pascoe 1999; Dixon and Dacre associated with local analgesia during standing surgery in 2005; duToit et al. 2008; Dixon et al. 2009). Removal via oral horses are rare and, to the authors’ knowledge, lingual extraction, repulsion or buccotomy (i.e. exodontia) is the trauma associated with anaesthesia of the inferior alveolar typical treatment recommended for severely diseased nerve in horses has not been previously reported. This teeth unresponsive to alternative treatments aimed at report describes self-inflicted lingual trauma in 3 horses salvaging the affected tooth (Gaughan 1998; Tremaine following anaesthesia of the inferior alveolar nerve for and Schumacher 2010). Apical dentoalveolar infections, standing oral surgery. supernumerary cheek teeth, diastemata with associated Case history severe periodontal disease, equine odontoclastic tooth resorption, hypercementosis of canine and incisor teeth Case 1 and a general belief that wolf teeth interfere with the bit are the most common reasons for exodontias (Easley A 14-year-old American Quarter Horse gelding presented 2004; Tremaine 2004; Staszyk et al. 2008; Tremaine and with a history of resistance to the bit and intermittent Schumacher 2010). With increased availability of bleeding from the mouth. During oral examination, a advanced instrumentation and practitioner experience mucosal injury in the right interdental space of the mandible *Corresponding author email: [email protected] just cranial to tooth 406 was observed. The canine teeth

(Triadan 04s) were very short and the owner commented a) that he regularly had them reduced by his farrier because he believed that they interfered with the bit. The right mandibular bar appeared slightly enlarged and the horse reacted to digital pressure applied to the area. Radiography of the mandible revealed lucency and resorption associated with the apical portion of tooth 404 and thinning of the mandibular cortex surrounding this tooth root. Extraction of tooth 404 was recommended and the horse was prepared for standing oral surgery. The horse was sedated with detomidine HCL (Dormosedan, 0.01 mg/ kg bwt i.v.)1 and 5 mg butorphanol tartrate (Butorphic, 0.01 mg/kg bwt i.v.)2 and repeat doses administered as needed to maintain sedation. The right inferior alveolar nerve was anaesthetised by advancing a 15 cm spinal needle from the ventral medial aspect of the horizontal ramus along the medial aspect of the ramus to a point of intersection of 2 imaginary lines: a horizontal line drawn through the occlusal surface of the cheek teeth and a perpendicular vertical line drawn through the lateral b) canthus of the eye (Tremaine 2007). A volume of 15 cc mepivacaine HCL (Carbocaine-V)1 was deposited at the site. The mouth was rinsed with a dilute chlorhexidine diacetate solution (Nolvasan)3. A McPherson dental speculum was placed to aid access to tooth 404. A mucosal incision was made caudal to the crown of tooth 404 and a Freer periosteal elevator was used to elevate the mucosa and disrupt the periodontal ligament. Ronguers were used to rotate the tooth in a horizontal plane and gradually loosen and remove it. The alveolus was flushed with dilute chlorhexidine solution and the mucosa sutured closed with 2-0 poliglecaprone 25 monofilament (Monocryl)4 in a simple continuous pattern. The horse was returned to the stall and offered hay when it appeared recovered from the effects of the sedative, approximately 2 h after the inferior alveolar nerve block had been performed. The horse was not reluctant to eat and no difficulty eating was observed or c) recorded during the time period after the sedation had worn off and the next examination. During oral examination the following day, it was discovered that the horse had macerated the right side of its tongue (Fig 1a). The mouth was flushed with dilute chlorhexidine solution and the horse discharged with instructions to continue flushing the mouth twice daily for 5 days and monitor for difficulties eating. The horse was returned for a re-examination and suture removal 2 weeks later. The owner reported that the horse had demonstrated no difficulties eating. The suture closure at the tooth 404 extraction site was partially dehisced but was healing by second intention. Wounds on the tongue were undergoing contracture and epithelialisation (Fig 1b) and near complete healing was observed during re-examination 6 weeks later (Fig 1c).

Case 2 Fig 1: Images of lingual trauma secondary to right-sided inferior alveolar nerve block in Case 1 the day following nerve blockade A 7-year-old Thoroughbred gelding was referred for (a), at 2 week (b) and 6 week recheck examination (c) where near resisting the bit and oral odour. Oral examination and complete healing of the tongue was observed.

radiographs revealed a deformed tooth 308 associated with diastema and periodontal disease. Oral extraction was recommended and the horse prepared for surgery. The horse was sedated with detomidine HCL (0.02 mg/kg bwt i.v.). The left inferior alveolar nerve was anaesthetised by advancing an 18 gauge, 13 cm needle as described in Case 1. A volume of 20 ml mepivacaine HCL was deposited near the site of the mandibular foramen. The tooth was extracted orally without complication and the socket packed with iodoform gauze (Curity packing strips)5. The horse was stalled and allowed access to hay when it appeared recovered from the effects of the sedative. No signs of reluctance to eat or difficulty eating was observed during the time period after the sedation had worn off and the next examination. The following day, a self inflicted wound on the left side of the tongue was observed during oral examination. The dental socket was re-evaluated and Fig 2: Oral examination of Case 3 the day following bilateral inferior the socket plugged with dental impression wax (Utility wax alveolar nerve blocks. Superficial abrasions to the dorsal and left strips)6. The oral cavity was rechecked 4 days later and the side of the tongue healed within 2 weeks without treatment. tongue lesion appeared static. The horse appeared to be eating normally. During re-evaluation at 7 weeks the socket discharged. Two week follow-up examination and appeared to be granulating well and the tongue wound treatment of tooth 309, found the tongue wounds was healed. completely healed with no scarring.

Case 3 Discussion

A 6-year-old Warmblood gelding presented with a draining The lingual and inferior alveolar nerves are branches of the tract from the ventral aspect of the right mandible. Oral mandibular nerve and arise as a common trunk that endoscopic examination revealed open pulp horns on passes rostrally between the pterygoideus medialis and the teeth 309 and 409. Radiographs showed apical blunting, ramus of the mandible. The lingual nerve separates from bone sclerosis and cement nodules indicative of periapical the inferior alveolar nerve at an acute angle where the disease associated with teeth 309 and 409. Bone lysis and inferior alveolar nerve enters the mandibular foramen and a tract leading to the right ventral mandibular cortex were traverses rostrally through the mandibular canal (Godinho associated with tooth 409. Extraction of tooth 409 and and Getty 1975) (Fig 3a). The sublingual nerve branches thorough assessment of the pulp horns of tooth 309 from the lingual nerve near the site where the lingual nerve with possible crown restoration or extraction was enters the root of the tongue. The sublingual nerve supplies recommended. The horse was prepared for standing oral sensory innervation to the mucous membranes of the surgery. Sedation was initiated with an i.v. bolus of tongue and floor of the mouth. At the root of the tongue, detomidine HCL (0.01 mg/kg bwt i.v.) and maintained with the lingual nerve ramifies to join the lingual branch of the a constant rate infusion (CRI) of detomidine (30 mg/kg glossopharyngeal nerve, collectively supplying motor and bwt/h) and butorphanol (16 mg/kg bwt/h) adjusted to sensory innervation to the tongue (Godinho and Getty desired effect (Goodrich et al. 2004). Bilateral inferior 1975). alveolar nerve blocks were performed as previously The inferior alveolar nerve is desensitised with local described using 20 ml mepivacaine HCL at each site. Tooth anaesthetic at the site where it enters the mandibular 409 was extracted with the procedure taking slightly more foramen. Because this site is in close proximity to the lingual than 4 h. Tooth 309 was not treated at this time. The tooth branch of the mandibular nerve, the lingual nerve may be 409 socket was packed with iodoform gauze, post desensitised with this block (Fig 3b). Most descriptions extraction. The horse was placed back in his stall and recommend volumes of 10–20 ml for this nerve block and allowed access to hay when it appeared recovered from suggest using a long acting local anaesthetic for the CRI sedative effects, approximately 4.5 h after the procedures lasting greater than 90 min (Fletcher 2004; inferior alveolar nerve blocks had been performed. No Tremaine 2007). Tremaine (2007) advised that horses signs of reluctance to eat or difficulty eating was observed undergoing analgesia techniques of the deeper nerves of during the time period after the sedation had worn off and the head should be observed for any adverse reactions or the next examination. Oral examination the following day self-trauma for 2 h following the procedure. Additionally, revealed superficial abrasions on the dorsum and left side Tremaine suggests withholding food during this period to of the tongue (Fig 2). The dental packing was removed prevent aspiration of feed or masticatory trauma to and replaced with dental impression wax and the horse desensitised oral tissues.

a) b)

Lateral canthus

Lingual nerve Mandibular nerve 90° Inferior Lingual nerve Mandibular Occlusal surface alveolar nerve nerve of cheek teeth Mandibular Mandibular foramen foramen

Medial PDG pterygoid muscle

Inferior PDG alveolar nerve Fig 3: a) Schematic drawing with the ramus of the left mandible removed to illustrate the close relationship of the lingual nerve to the inferior alveolar nerve at the mandibular foramen. b) Schematic drawing illustrating the location of anaesthetic placement at the intersection of a horizontal line through the occlusal surface of the cheek teeth and a perpendicular vertical line through the lateral canthus to perform a left inferior alveolar nerve block.

Local anaesthetics are commonly classified by their more commonly than previously thought. Fortunately, speed of onset and duration of action. These factors self-inflicted injuries to horses’ tongues appear to heal influence their selection for clinical use. Lidocaine readily with minimal or no treatment necessary. The (Xylocaine) and mepivacaine HCL (Carbocaine) both horses in this report with self-inflicted lingual trauma did have a rapid onset of action but a different duration of not require significant treatment of their injuries. Although action of 60–120 and 90–180 min, respectively (Skarda and uncommon, a bilateral inferior alveolar nerve block Tranquilli 2007; Fischer 2009). The onset of action of local was performed in Case 3 due to the presence of anaesthetics is inversely related to the lipid solubility and diseased teeth in both mandibular arcades. It is possible acid dissociation constant (pKa). The duration of action that with bilateral inferior alveolar nerve blockade with of a local anaesthetic is related to its lipid solubility and concomitant bilateral lingual nerve anaesthesia, lingual level of protein binding within the axonal membrane. trauma could be more extensive. Mepivacaine HCL is more highly protein bound compared In conclusion, a short acting anaesthetic such as to lidocaine and, therefore, has an increased duration of lidocaine should be used when performing an inferior action (Skarda and Tranquilli 2007; Fischer 2009). alveolar nerve block whenever possible depending on Since the lingual nerve is likely to be anaesthetised length of procedure. Accurate needle placement and the when the inferior alveolar nerve is anaesthetised the use of a smaller dose of anaesthetic might decrease authors’ advise that a short-acting local anaesthetic, the chance of anaesthetising both nerves and reduce the such as lidocaine, should be used whenever possible possibility of lingual trauma. Bilateral inferior alveolar nerve depending on the anticipated length of the procedure. block could potentially result in complete desensitisation of Additionally, accurate placement of the needle and use the tongue and more severe self-inflicted lingual trauma. of a smaller volume of anaesthetic (10 ml) may avoid No outward clinical signs of lingual trauma was observed desensitisation of the lingual nerve and prevent this in the horses in this report and therefore it is important complication. In cases where lingual nerve blockade is to examine horses post operatively for lingual trauma suspected, horses should be re-sedated and a full following use of inferior alveolar nerve blockade. mouth speculum maintained in place at the end of the procedure to prevent this complication until sensation Authors’ declaration of interests returns to the tongue. This is especially important following an inferior alveolar nerve block with mepivacaine HCL. No conflicts of interest have been declared. Horses undergoing mandibular tooth extraction procedures may not routinely be subjected to oral Acknowledgements examinations the day following extraction. Since the horses in this report had no clinical signs of lingual trauma The authors graciously thank Dr John Schumacher for his and the injury was only discovered during later assistance with preparation of this case report and Dr Phillip examination, it is likely that this complication may occur Garrett for providing medical illustrations.