The Whole Tooth and Nothing But the
Truth
Eric M. Davis, DVM, FAVD, Dipl. AVDC
This series on oral care and dental disease is provided by Eric M. Davis, DVM, a
Diplomate of the American Veterinary Dental College. Dr. Davis is the former
Director of the Dental Referral Service at the Cornell University Hospital for
Animals, and is currently the Director of Animal Dental Specialists of Upstate New
York, a referral clinic for veterinary dentistry and oral surgery located in
Fayetteville, New York. Dr. Davis can be contacted at emdavis@adsuny.com or at
315-445-5640.
Pain, Pain, Go Away
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 pain are 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 that the 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 tooth
reliably 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 so awful, 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 because they 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 examined the 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 understood to 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.vsag.org, sponsored
by the Veterinary 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 shortlived, 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, low doses 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 subtle behavioral 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!
1
Malamed SF. Management of pain and anxiety. In: Cohen S, Burns RC, eds. Pathways of the Pulp 7th Edition. St.
Louis: Mosby, 1998; 657-673.
2
Weigelt A, Terekhin P, Kemppainen P, Dӧrfler A, Forster C. The representation of experimental tooth pain from
upper and lower jaws in the human trigeminal pathway. Pain 2010; 149 (3): 529-538.
3
Brown DC, Bernier N, Shofer F, Steinberg SA, Perkowski SZ. Use of noninvasive dolorimetry to evaluate analgesic
effects of intravenous and intrathecal administration of morphine in anesthetized dogs. Am J.Vet.Res.2002; 63
(10): 1349-1353.
4
Neiburger EJ, Patterson BD. The man-eaters with bad teeth. NYS Dent J 2000; Dec. 26-29.
5
Rochette J. Regional anesthesia and analgesia for oral and dental procedures. In: Holmstrom SE, ed. Dentistry.
Vet Clin of N. Am. 2005: 1041-1058.