Pain Management for Veterinary Dental Patients

In the past 10 years, the delivery of quality veterinary care in general practices, particularly with regard to professional dental care, has made great strides. The increased prevalence of dental radiology in general practices is just one example of the forward progression of veterinary dentistry. Continuing education in veterinary dentistry is in great demand as veterinarians and veterinary technicians strive to provide the best care for their patients. Courses offered by veterinary dental experts include instruction in dental radiology, surgical extraction, and periodontal therapy, as well as basic prophylactic and charting skills. All of these skills are crucial to maintaining a high standard of care for dental patients.

Pain management is also a critical component of a comprehensive dental service. This article gives an overview of the physiology of pain, offers a discussion of a variety of analgesic agents, and provides information to help create an effective pain management protocol for dental patients.

The Importance of Managing Dental Pain

Effective pain management before, during, and after a dental procedure can significantly improve care and raise the bar for dentistry services provided in general practices. A number of positive outcomes are achieved when the patient is comfortable and pain free. During the procedure, benefits of pain management, specifically regional nerve blocks,¹ include the ability to maintain the patient at a lighter plane of anesthesia, significantly reducing the anesthetic risk to the patient. Pain management after the procedure, including medications administered at home, promotes a smooth postoperative recovery for the patient and can increase client compliance with continued, regular professional prophylactic dental cleaning and evaluation.

Client compliance with follow-up care is especially important for patients with periodontal disease, which occurs in approximately 80% of dogs and 70% of cats over the age of 2 years.² These patients require frequent (every 4 to 6 months in some cases) professional cleaning, assessment, and treatment to successfully manage periodontal disease. If a patient undergoes oral surgery and is not properly treated for pain, it will likely exhibit obvious signs of pain at home after the procedure. These signs may include whining, groaning, excessive drooling, and inappetence. It is highly unlikely that the owner will continue with follow-up professional care after seeing their pet in pain. Lack of follow up will lead to undue patient suffering as dental disease progresses without professional assessment and treatment.

Classifications of Pain

Pain is classified based on the origin of the pain impulse or its physiologic importance.

Clinical pain occurs when peripheral nerves or the spinal cord are injured, subjecting nociceptors (pain-sensing neurons) to repeated impulses without the benefit of analgesia, ultimately resulting in central sensitization, also called the wind-up phenomenon (BOX 1).

Peripheral pain can include either visceral (thoracic or abdominal) or somatic pain involving the joints and muscles. Visceral pain is characterized by a cramping sensation and is poorly differentiated. Somatic pain, on the other hand, is localized and manifests as an aching or throbbing sensation. As an example, patients experience somatic pain after a spay surgery or other abdominal surgical procedure.

Neuropathic pain occurs when peripheral nerves or the spinal cord are damaged and is felt as an intermittent burning sensation. Cancer patients that are treated with radiation therapy and patients that have undergone limb amputation experience this type of pain.

Idiopathic pain exists without a definitive cause and is often associated with stress and behavioral changes in the patient.

Physiologic pain is caused by a painful stimulus introduced at the peripheral nerves. This type of pain is also known as teaching pain.⁴ It is immediate and sharp and “teaches” the patient to protect itself from whatever is causing the pain. To illustrate, imagine a 2-year-old child who touches a hot burner on the stove and pulls his hand back quickly to avoid further injury. Oral pain, whether caused by dental disease or by treatment of dental disease, falls into this category; therefore, this type of pain will be discussed further in this article. Physiologic pain, if not managed successfully, can quickly become clinical pain.⁴

Signs of Pain

The physiology of pain in animals is very similar to that in humans; that is, animals experience and feel pain similar to the way humans do.⁵ However, animals typically do not exhibit pain responses as humans do. They can be stoic, or hide their reaction to pain.

When an animal sustains an acute injury, obvious pain behaviors such as vocalization (e.g., whining, groaning) are easily recognized. Patients may limp or flinch when palpated. Patients with dental pain can be much more difficult to assess because they tend to suffer in silence. Dental conditions like fractured teeth can be excruciating, but these patients may not show any signs of pain or may exhibit very subtle changes in behavior. Slight changes in posture, drooling, squinting, staring, hiding, lethargy, and even purring can indicate oral discomfort.

Recognizing these signs can be challenging, and they are sometimes missed as pain responses. Changes in behavior in older pets, such as decreased appetite and activity, are often perceived by owners as the pet “just slowing down” in its later years. However, in many cases, these patients have long-term oral pain secondary to prolonged, untreated dental disease. Once the disease is treated and pain is managed or eliminated, these patients exhibit many positive behavioral changes, as described by many owners during recheck appointments.

Almost all procedures that are used to treat dental conditions can induce varying degrees of pain. Dental procedures as minor as ultrasonic scaling or root planing can cause mild to moderate pain. More involved procedures, including surgical extraction, en bloc resection, and mandibulectomy, can cause severe pain. If postoperative pain is not managed well during recovery and the days following the procedure, it can be detrimental, especially in older patients or patients with mildly compromised organ function such as liver or kidney disease.⁶ However, in patients with preexisting chronic conditions like renal or liver disease, drug choices can be limited. For instance, nonsteroidal anti-inflammatory drugs (NSAIDs) should be used with caution or avoided in these cases. All scenarios from mild to severe pain must be addressed appropriately for the overall well-being of the patient.

Physiology of Pain

To implement successful analgesic protocols, it is helpful to know how pain is transmitted and eventually perceived by the patient. Understanding this “pain pathway” is the key to providing effective pain management.

The physiologic process of the pain response consists of 3 main components culminating in perception of pain by the cerebral cortex, essentially recognition of pain by the patient, or nociception. It begins with the noxious stimulus or, more simply put, the painful event at the site of injury or surgical site. The stimulus is translated from physical energy into an electrical impulse at the peripheral nerves. This process is known as transduction.

Transmission then takes place as the electrical energy is transmitted by nerve fibers through the peripheral nervous system. Two primary nerve fibers are involved in transmission. A-delta fibers conduct fast pain, recognized by the patient as the first sharp, stabbing pain sensation. C fibers conduct slow pain, recognized as a dull, throbbing pain.

As the painful stimulus is transmitted and eventually reaches the spinal cord, modulation can take place. Endogenous systems located within the spinal dorsal horn, including opioid, serotonergic, and noradrenergic systems, can inhibit or lessen pain. In other words, modulation enables the patient to lessen its own pain to some degree.

Perception of pain by the patient is the end result of transduction, transmission, and modulation.⁷ Each of these processes of the pain pathway is susceptible to the effects of a variety of analgesic agents available to veterinarians.

Pain Medications

Classes of analgesic agents include opioids, alpha-2 agonists, NSAIDs, local anesthetics, and adjuvant analgesics.

Opioids

Opioids are classified by the effect they have on specific receptors. Mu receptors, located on the second-order neuron within the spinal cord (where modulation takes place), are responsible for the most profound analgesia within the body. When an agonist—an agent that enhances a receptor—is introduced and binds with the receptor, the analgesic effect is significantly increased, thereby relieving pain for the patient. The most common examples of pure mu agonists available are listed in TABLE 1. These agents are used for more severe pain or as a premedication before surgical procedures and can be administered intravenously, intramuscularly, transdermally, or orally. However, these opiates can produce dysphoria (anxiety) and/or hyperthermia, and caution should be used when using pure mu agonists in cats.

Buprenorphine (0.005–0.02 mg/kg) is considered a partial mu agonist (i.e., it only partially stimulates the receptor), making it less effective than the pure mu agonists, and is used for mild to moderate pain. This drug is used more commonly for cats to avoid the adverse effects of pure mu agonists. Buprenorphine can be administered intravenously, intramuscularly, subcutaneously, or orally.⁸

Butorphanol (0.2–1.0 mg/kg) is a mu agonist/antagonist. It simultaneously enhances and blocks the mu receptor, making it less effective than a pure mu agonist. In addition, the duration of this agent is relatively short, lasting only 1 to 3 hours. More involved dental procedures often last up to 2 hours. If butorphanol is used as a premedication, the surgical procedure could potentially outlast the analgesic, causing the patient to recover without the benefits of analgesia. Because of its lesser efficacy and short duration, butorphanol is not recommended as an effective analgesic for dental procedures.⁸

Alpha-2 Agonists

Alpha-2 agonists include xylazine (0.1–0.5 mg/kg) and medetomidine (1–10 ug/kg), which enhance the alpha-2 receptor on the first-order neuron. These agents can sometimes cause adverse cardiac effects, specifically severe bradycardia. Medetomidine should be used with caution or even avoided, especially in patients with underlying cardiac issues.⁸

NSAIDs

NSAIDs prevent the formation of prostaglandins by targeting the cyclooxygenase enzyme responsible for prostaglandin production. Prostaglandins are known to lead to inflammation and pain as well as to affect peripheral nociceptors, causing peripheral pain. Carprofen (4.4 mg/kg once daily), meloxicam (0.2 mg/kg initially; 0.1 mg/kg once daily), and ketoprofen (1.0–2.0 mg/kg) are the more commonly used NSAIDs in veterinary medicine. They are available as injectable and oral formulations.⁸

Local Anesthetics

Local anesthetics prevent the conduction of nerve impulses from the surgical site. Lidocaine (7 mg/kg maximum per site)8 and bupivicaine (1.0 mg/kg)⁸ can be used alone or simultaneously. However, it is important to note that lidocaine has a much shorter duration of action (1–2 hours) than bupivacaine (up to 6 hours).

Adjuvant Analgesics

Adjuvant analgesics are agents that are used for other applications but have been found to have beneficial effects in relieving certain painful conditions. Antidepressants, neuroleptics, and anticonvulsants are a few examples. N-methyl-D-aspartate (NMDA) receptor antagonists also fall into this group. Ketamine (injectable) and gabapentin (oral) are commonly used as NMDA antagonists.

Analgesic Strategy for Dental Patients

Anesthetic Premedication

The first step to an effective analgesic strategy starts with what is known as preemptive analgesia, in which an analgesic is introduced before the patient is exposed to noxious stimuli. A narcotic such as an opiate, along with an NSAID in some instances, is usually administered as preemptive analgesia. Proactive administration of an analgesic before the dental procedure begins can help the patient avoid postoperative clinical pain. Increasing the modulation taking place in the spinal dorsal horn more effectively controls pain, thereby preventing central sensitization or wind up, which can otherwise occur during recovery (BOX 1).

Regional Nerve Blocks

Regional nerve blocks deliver the anesthetic agent in or near a foramen where the target nerve bundle is located to block sensation in a specific region in the oral cavity. The most widely used sites for placing a nerve block during dental procedures are the infraorbital foramen, the caudal maxillary region, the inferior alveolar foramen, the middle mental foramen, and the inferior alveolar foramen. The technique is as simple as giving an injection. Proper placement of the needle to deliver the agent to bathe the nerve bundle sufficiently is where most of the challenge exists. However, with proper instruction in a wet lab setting, and with additional practice on cadaver specimens, this skill can be relatively easy to master.

Regional nerve analgesia is absolutely essential to the dentistry service for quality patient care. To illustrate this point, consider that when a patient feels pain while under anesthesia, its heart rate, respiratory rate, and blood pressure increase. The patient may even attempt to move if the anesthesia is too “light.” The anesthetist is alerted by these changes and immediately reacts by increasing the gas inhalant to produce a deeper plane of anesthesia for the patient so that the procedure can be completed. Deeper planes of anesthesia can compromise cardiac output, blood pressure, and respiration. When nociception is prevented with an efficiently placed nerve block, the patient does not experience changes in heart rate, respiratory rate, or blood pressure and, consequently, can be maintained at a much lighter plane of anesthesia.

Balanced Analgesia

The bulk of a successful analgesic strategy consists of a multimodal or “balanced” approach. Balanced analgesia is defined as using agents from two or more drug classifications simultaneously to modulate the pain impulse as it travels the pain pathway. By interrupting transduction and transmission as well as heightening the effects of modulation within the spinal cord, balanced analgesia provides optimum pain relief. BOX 2 outlines a specific plan of when and where to use analgesic agents in a successful pain management strategy, keeping in mind the pain pathway processes and the interruption of the pain stimulus. Patients that have a pain-free recovery are less likely to experience central sensitization. Pain behaviors during recovery, including vocalization and thrashing, are also eliminated.

Client Communication

Anesthesia of a pet is a substantial fear and source of anxiety for most pet owners when dental procedures are recommended and is often the reason why owners do not follow recommendations for professional dental cleaning, assessment, and treatment. Educating clients on the positive effects of the practice’s comprehensive analgesia strategy, including the benefits of regional nerve analgesia (i.e., use of a lighter plane of anesthesia), can reduce these fears.

Home Care

In most cases, regional nerve blocks will most likely still be in effect during recovery and even when the patient returns home. In addition, any injectable NSAID administered will also still be providing analgesia, as the duration of action of injectable NSAIDs can last up to 24 hours. Owners are pleasantly surprised when their pet eats and remains comfortable throughout the evening following its dental procedure. Again, this can increase client compliance with the follow-up professional dental care necessary to successfully manage periodontal disease.

Pain management needs to continue in the days following the dental procedure. Several options, including chewable tablets, oral liquids, and transdermal patches, are available to administer postoperative analgesics. An opiate given in conjunction with an NSAID creates a synergistic effect, providing a more profound analgesia for the patient.⁷

Conclusion

Implementation of a pain management protocol should involve the entire veterinary team. Although this article provides an introduction to many aspects of pain physiology and management, a complete discussion of pain management in the dental setting is beyond the scope of a single article. Continuing education courses, including lectures, wet labs, and online webinars, are offered for this particular subject, as well as for other disciplines in veterinary dentistry. To maintain a high level of care for dental patients, veterinary technicians should take advantage of available continuing education opportunities. Ultimately, the patient reaps the benefits of implementing an effective analgesic protocol.