Oral/dental disease (especially periodontal) is typically a slowly progressive and chronic disease process. Human studies suggest that periodontal disease is actually only painful in a small number of affected patients. However, some patients report dull, localized and radiating deep jaw pain due to periodontal disease. In addition, pain is consistently reported where root exposure has occurred secondary to cementum destruction. Food impaction also causes varying degrees of discomfort (but can be significant). Further, there are numerous painful conditions which are common in veterinary patients including tooth fractures, caries, tooth resorption, attrition, enamel hypocalcification, and traumatic malocclusions. In humans, periodontal disease is more prevalent in compromised socioeconomic areas where oral hygiene is not routinely practiced. From the standpoint of oral neglect, our patients resemble this human subset. A recent study revealed that 96% of the homeless people in Hong Kong had periodontal disease. The dental problems most frequently reported in this population were bleeding gums or drifting teeth (62%), dental pain (52%) and tooth trauma (38%).iv

Although direct assumptions of the source of pain cannot be made, there is likely a higher prevalence of pain in our animal patients.

Several species differences must be considered when viewing oral disease in veterinary patients.
1. Canine small breeds often present with profound soft tissue destruction and bone loss.
2. Food and other foreign body impaction are significantly more likely due to severity and size of the periodontal defects in veterinary patients.
3. Cementum destruction results in root exposure creates sensitivity.

Chronic pain
Veterinary patients with severe or unusual types of periodontal disease (e.g caudal stomatitis) are suffering from chronic pain. Special preparation and techniques should be used when managing these cases surgically. Recognizing not only the pain at the site of inflammation, but also the often neglected central pain mechanisms, is important when managing these patients. Initiating acute surgical pain to chronically diseased painful tissue heightens the pain response creating a patient that is difficult to manage post-operatively.

Management strategies
Preemptive analgesia is more effective than post-operative, and it is therefore important to administer the drugs before the painful procedure. Depending on patient health, a multimodal approach should be employed, as this provides superior analgesia.

Regional nerve blocks
An additional, critical method of pain management is regional anesthesia (also known as local nerve blocks). When correctly administered, regional nerve blocks provide not only elimination of pain perception in the innervated tissue but also positive systemic effects. Proper blockade of oral tissues prior to surgical manipulation eliminates central perception allowing anesthetic planes similar to that for non-painful procedures. This reduction in the percentage of inhalant anesthetic will have positive effects on intraoperative physiology.
This includes minimizing:
• Hypotension
• Hypoventilation
• Bradycardia.

If proper perfusion is maintained, normothermia becomes easier to achieve. Blood pressure, heart rate and respiration rate should remain stable upon surgical insult if blocks have been administered properly and adequate onset time from administration has elapsed. If these parameters increase, the block is not effective or insufficient time to onset was allowed. If the proper time has definitely passed, the block may be repeated providing that the maximum total dose is not exceeded.
Intravascular administration must be avoided. Aspirating prior to injection will ensure that the agent was given outside the vasculature. Excessive systemic uptake or intravascular administration could cause CNS or cardiovascular complications.

There are two agents which are commonly employed for regional anesthesia: lidocaine and marcaine. Lidocaine has the distinct advantage of fast onset (1-2 minutes) but only lasts 30-60 minutes. Therefore, it does not provide adequate analgesic duration in lengthy procedures. In addition, it offers only minimal if any pain relief in the postoperative period. Conversely, bupivacaine’s analgesic effect is significantly longer in duration (6-8 hours). The concern with its use has been that it was thought to have a longer onset of action, however, recent studies reveal efficacy in as little as 4 ½ minutes. The desire of short onset with longer duration made combining the products a popular option. However, recent research has shown that the combination may result in decreased efficacy.

All local anesthetic agents are vasodilative, and therefore create faster removal from the area and thus a shorter duration of action. Adding epinephrine to local agents has been shown to increase the active time by up to 50%. Adding an opioid such as buprenorphine or morphine to a bupivacaine block may result in a doubling the time of effect of bupivacaine alone. This author utilizes plain marcaine exclusively as 6-8 hours is sufficient time for effect for patient comfort without lasting too long into the post-operative effect that eating may be compromised. While there is some concern with marcaine use and cardiotoxicity in cats, if intravenous injection and overdosage is avoided, this complication should not occur. For this reason, it is critical to aspirate prior to each injection of local anesthetic. If blood is encountered, the needle should be redirected (and reaspirated) to insure that intravenous (or intra-arterial) injection is not inadvertently performed.

Recommended infusion volumes vary from 0.1ml – 1.6 ml from small to large patients. As far as dosage of local anesthetics is concerned, the published recommended maximum total dose of local anesthetics is 2 mg/kg (single agent or combination). This level is easy to reach in small patients when utilizing 2% lidocaine in feline and small and toy breed dogs. For example, a 5 kg patient should receive a maximum dose of 0.5 cc of 2% lidocaine. For this reason, it is advised to dilute this product to decrease the possibility of overdosage. This author has never experienced complications at these dosages. Clinically, prehension and mastication does not appear to be compromised postoperatively in dogs and cats receiving dental blocks even if all four quadrants have been blocked. These guidelines are being reviewed, as the published maximum dose is based on intravenous injection and some anesthesiologists are utilizing much higher dosage for local injection.

The three major blocks are the infraorbital, mental, and mandibular. Some dentists/anesthesiologists utilize the caudal maxillary block, but this author does not recommend it due to the increased possibility of orbital penetration. If properly performed, the infraorbital block can effectively anesthetize the entire ipsilateral maxillary quadrant.

The depth to which the needle is placed within the foramen is one of significant debate. Some dentists recommend that the foramen be barely or not entered, while others will place the needle very deep within the infraorbital canal to block the molar teeth. I tend to be somewhere in between (see individual blocks below).

Infraorbital block
The infraorbital block is highly effective for the ipsilateral maxilla and teeth as well as the associated soft tissues. The infraorbital canal runs rostrally just above the apices of the maxillary fourth premolar and exits the maxilla over the distal root of the third premolar. To approximate the dorso-ventral location it is helpful to imagine the fourth premolar as being approximately the same size mesio-distal as corono-apical. Therefore, measure the width of the tooth and then measure that distance dorsally from the cusp tip. The infraorbital canal is just apical to this point. The foramen is easily palpated, especially in cats and large breed canines. Manually retract the lip and the infraorbital neurovascular bundle dorsally. Advance the needle in a caudal direction close to the maxillary bone and just ventral to the retracted bundle to a point just inside the canal (and up to the medial canthus of the eye). The needle should pass into the canal without engaging bone. In feline patients, the infraorbital canal is VERY short, which allows for orbital penetration. For this reason, we recommend that the foramen be barely entered and the needle directed ventrally. In dogs, do not advance past the medial canthus of the eye. The block will diffuse distally to the molars if a finger is placed over the foramen for 30-60 seconds after injection.

Mental Block
The middle mental foramen is located apical to the mesial root of the second premolar in the dog, and in the halfway in the diastema between the canine and third premolar in the cat. It is approximately 2/3 of the way down from the dorsal border of the mandible. This will anesthetize from the ipsilateral mandibular third premolar to the central incisor and the surrounding bone and associated soft tissue. The mandibular labial frenulum is retracted ventrally and the needle is inserted at the rostral aspect of the frenulum and advanced at an approximate 45 degree angle along the mandibular bone to just enter the canal.

Mandibular Block
The inferior alveolar nerve enters the mandibular foramen on the lingual aspect of the caudal mandible. The caudal mandibular block is performed by infiltrating the nerve at this level prior to its entry into the canal. This author tends to perform this block intraorally. The patient is placed in dorsal recumbancy and the mouth opened. With the index finger of the non-dominant hand, feel the notch on the ventral aspect of the caudal mandible. Then slide the finger a bit dorsally on the lingual aspect. Measure the width of the third molar and enter the mucosa right on the lingual aspect of the mandible at a point that far back from M3. Insert on a 45 degree angle advancing along the bone until the needle is felt moving through the tissues and inject at this point. If correctly performed, all mandibular teeth, bone, and soft tissue on the treated side are affected by this block. Exceedingly rarely, patients who are not monitored postoperatively can cause severe trauma to the tongue during the recovery period. Whether this is specifically associated with regional anesthesia or recovery from any procedure is not reflected in the literature. To wit, this author has seen it twice in 15 years, both were boxers, and one did not even have blocks performed. In any case, proper patient monitoring during recovery should preclude this problem.

Conclusions
The vast majority of veterinary dental patients have some to significant oral pain which is acutely worsened with therapy (especially extractions). Proper pain management will decrease MAC and the secondary negative effects of increased inhalational anesthetics as well as smooth recovery.
A multimodal approach, including regional anesthesia, is ideal. Finally, pre-emptive analgesia is superior to attempting to manage pain which has already been perceived.