The Whole Tooth and Nothing But the Truth

Pain, Pain, Go Away
 

Eric M. Davis, DVM, FAVD, Dipl. AVDC

As I reflect on my 32 years as a veterinary practitioner, I am proud to have witnessed our profession transition from a prevailing attitude that “animals do not experience pain as do humans”, to the recognition that pain management is one of our most important responsibilities as animal health-care providers.  Although most owners and veterinarians can recognize obvious behavioral or physiological changes manifested by animal patients as indicators of discomfort, the signs are often subtle. Since an animal’s behavior must be subjectively interpreted by humans, opinions regarding the level of pain perceived by animal patients may vary, in part because humans have their own biases. Some humans prefer to “tough it out” and not rely on drugs to mitigate pain, whereas other humans plead, “give me the drugs” because of fear, anxiety, or because they genuinely prefer to experience as little discomfort as possible. Thus our own perceptions about pain, and how we prefer to treated when an injury or illness occurs, may strongly influence how we manage pain in our patients.

For many humans, the association between dentistry and painare inextricably linked. Studies have demonstrated that one of the major reasons why over 50% of adult Americans do not routinely seek dental care is a fear of pain.[1]A toothache is often described verbally by affected humans as “sharp, shooting pain”, especially when the tooth is touched by a metal instrument or by a stream of cold air. Do animals perceive pain in the same way? A recent study used functional MRI to examine the cerebral cortices of human volunteers while researchers applied short, electrical pulses to either an upper or lower tooth.[2]  The electrical pulses were regulated so thatthe volunteers verbalized that the pain intensity was approximately 60%, (an intensity of 100% was considered to be “the worst pain imaginable”). The result was that regardless of whether an upper tooth or a lower tooth received the electrical stimulation, the identical parts of the brain responded (do NOT try this at home). Thus, irrespective of whether the mandibular branch or the maxillary branch of the trigeminal nerve was stimulated, the brain perceived the information without being able to localize the source. The researchers concluded that their experiment might help explain why some human patients are unable to locate which tooth is the painful one.  Although the purpose of the study was different, a similar experimental design was used in anesthetized dogs to objectively evaluate the analgesic effect of morphine. In a study performed at the University of Pennsylvania School of Veterinary Medicine, researchers applied an electrical shock to the canine teeth of anesthetized dogs.[3] Stimulation of a toothreliably caused a “jaw opening reflex”. Since pain is reportedly experienced by humans who allow a tooth to be electrically stimulated, and since intradental nerves (sensory branches of the trigeminal nerve) in cats, dogs, and monkeys have been shown to function in the same manner as intradental nerves in humans, the researchers theorized that the jaw opening reflex could be used to objectively measure pain (termed “dolorimetry”) without actually inflicting pain in a conscious animal. To further confirm that electrical stimulation of a tooth was actually associated with a pain response, both intravenous and intrathecal administration of morphine, resulted in inhibition of the jaw opening response, but similar injections of saline had no effect on the response to dental electrostimulation. Thus, it is reasonable to conclude that the perception of dental pain is similar in humans and in dogs.

Because dental pain is considered by most humans to be soawful, owners can readily appreciate that oral disease in their pets might similarly be painful. The “disconnect” is that animals do not complain, and signs of oral pain are often subtle and not easily recognized by human caretakers. That does not mean animals do not perceive the pain, they do…but they do not have an effective way to complain. The majority of owners believe intuitively, that animals experiencing oral pain should stop eating. To the contrary, most household dogs and cats with dental pain continue to eat becausethey do not use their teeth to either prehend or chew their food like humans do. Dry, pelletized food is generally swallowed without chewing each particle. As proof, listen carefully as your pets eat, or study the vomitus when your cat pukes on the carpet.  The occasional particle may get chewed, but the vast majority of particles are merely swallowed whole, without chewing.

The situation is different when non-domesticated carnivores,who must rely on their dentition to capture and consume prey, experience dental pain. It has been theorized that the underlying reason why two lions ate 135 railway workers in 1898 in what is now Tsavo National Park in southeastern Kenya was because of dental pain.[4] Forensic dentists examinedthe skulls and determined that one lion had a fractured mandibular canine tooth with radiographic evidence consistent with associated periapical osteomyelitis. Examination of the skull of the second lion revealed that the animal had sustained a fracture to a maxillary fourth premolar tooth that resulted in exposure of the pulp chamber. Evidence of periapical bone infection was not identified, indicating that the pulp exposure was of rather recent origin. The researchers suggested that dragging a sleeping human from a tent was easier and resulted in less risk for additional oral injury than pursuit of usual prey animals that could defend themselves with hooves, horns, or antlers.

Thus, as animal healthcare providers, please ask yourself“If that situation were present in my body, how much discomfort would I experience?” How would I wish to be treated? Please recognize that conditions that would likely result in pain for you, are similarly experienced by animal patients even if their behavior SEEMS “normal”. Broken teeth are painful and represent a direct pathway for invasion by microorganisms from the contaminated oral cavity to deeper body parts, such as bone (osteomyelitis), soft tissues (cellulitis) and the systemic circulation (septicemia). Oral inflammation associated with stomatitis, moderate to severe periodontal disease, and malocclusions that result in abnormal tooth to tooth, or tooth to soft tissue contact, all represent sources of pain to the patient (inflammation = rubor (redness), calor (heat), tumor (swelling), and dolor (PAIN). Pain relief is therefore a crucial aspect of patient care, before, during, and after treatment. “So”, as my grandfather used to ask me, “Vat’s new?” 

Perception of painful stimuli by the brain is now understoodto be a very complex interaction with multiple levels of redundancy. The most effective pain control is delivered when more than one drug is used to modulate the perception of pain at different places along the pain pathway.  This concept is often referred to “multimodal analgesia”. Another useful concept is “preemptive analgesia” which refers to blocking the paths of pain perception before pain actually occurs, thereby diminishing the potential for modulation and magnification of pain signals to the brain. Extremely valuable information may be found at www.vasg.org, sponsored by theVeterinary Anesthesia and Analgesia Support Group where practical drug protocols, techniques, and monitoring equipment useful in small animal practice are described.  As examples of these concepts, the typical anesthetic protocol used at Animal Dental Specialists of Upstate New York, includes pre-anesthesia administration of a pure mu agonist, such as hydromorphone, and a benzodiazepine, such as midazolam, to preemptively provide significant analgesia and mild sedation to the patient prior to IV catheter placement. Twenty minutes after injection of the first two drugs, an intravenous catheter is placed, and general anesthesia is induced with propofol and maintained with isoflurane and oxygen, delivered via a cuffed endotracheal tube. Regional nerve blocks are then administered (prior to anticipated oral surgery) using a combination of both lidocaine and bupivicaine. The lidocaine has a rapid onset of effect but is short-lived, while bupivicaine takes longer to cause “numbness” but the effect lasts up to 6-8 hours. The regional nerve blocks prevent local sensory nerves from transmitting information that painful stimulation has occurred, and thereby reduces the level of general anesthesia necessary to block the perception of pain. Provided there are no contraindications to their use, a peri-operative injection of an NSAID is often administered to dogs (not to cats) undergoing dental procedures, to reduce inflammation by blocking prostaglandin production through inhibition of the enzyme, cyclooxygenase (COX).[5] Post-operatively, lowdoses of an alpha-2 agonist, such as dexmedetomidine, may be administered to provide additional sedation, analgesia, and muscle relaxation. Either hydromorphone or buprenorphine, a partial mu agonist, is administered three hours following the initial pre-anesthetic dose of hydromorphone, to maintain effective pain control. Earlier administration of buprenorphine may result in diminished analgesic effect because of competitive binding onto mu receptor sites by the previously administered hydromorphone. Post-operatively, trans-mucosal buprenorphine, tramadol, and/or gabapentin may be dispensed for oral administration for three to five days following oral surgery. 

Even though most owners do not recognize the subtlebehavioral changes exhibited by their pets as a result of painful dental disease prior to treatment, I am told nearly every day, how much the health and activity level of pets has been improved following dental treatment. “I didn’t realize how much it must have been bothering her” is an often heard refrain. And that feels good!