Introduction

For many people, the scariest part of a reptile is its open mouth, preparing to bite. For the veterinarian, the scariest part is often the opposite, trying to get that mouth to open. The oral cavity is often one of the first parts of a reptile that one can see, so disease associated with the oral cavity is more quickly noticed, Sometimes it is the fact that the animal is refusing to eat, in effect, not opening its mouth when it should be that brings the animal into the veterinarian.

Anatomy

Squamates (snakes and lizards) have a kinetic skull, so they can raise their upper jaw as a hinge to increase gape during feeding. The quadrate bone that articulates between the upper and lower jaw also moves freely.In lizards, the internal nostrils lie rostrally so that incoming air must pass through the mouth on the way to the larynx. Snakes can protrude the glottis and trachea out of the mouth while feeding. Chelonia and crocodiles (and some lizards) have a hard palate that separates air flow from the oral mouth.² The mandibular rami are connected in snakes by an elastic ligament, allowing greater flexibility for snakes to ingest prey to compensate for the lack of hands and inability to bite off pieces of food.

Reptile teeth have enamel, dentine, and cement but no periodontal membrane. There are three categories of reptile teeth: acrodont, pleurodont, and thecodont. Acrodonts (like water dragons and chameleons), have teeth attached to the crest of the bone. Pleurodonts (snakes and iguanids) (sometimes referred to as modified thecodonts)have an eroded lingual side and are attached to a higher sided labial wall. (This is common in snakes and lizards like iguanas). True thecodonts (crocodilians)have teeth embedded in a deep bony socket but there is no periodontal membrane. Reptile teeth are resorbed and replaced at a rapid rate throughout life. This is called polyphyodonty. Because of their simple structure, they need frequent replacement to keep them sharp. For pleurodonts, the new tooth lies lingual to the old tooth and replacement occurs in a wave-like pattern from back to front. However, many acrodont reptiles cease producing new teeth after a certain time, using the remaining teeth and jaw margins after these have been worn away.² Crocodilians can have their replacement teeth come in at strange angles initially, as if abnormal; however, the tooth generally straightens in a short bit of time. Chelonians of course have no teeth, instead having a keratinized beak more like a bird.

Many reptiles lack lips, so they rely on their jaw, and sometimes the tongue, to apprehend food. Mastication is far less than in mammals. Reptiles have a complex system of oral secretory glands to help them lubricate their prey. Crotalids, elapids, some colubrid species, and helodermatid lizards have modified these salivary glands into venom glands like Duvernoy's gland to help immobilize the prey.² Over time, many more lizard species have been found to be venomous such as bearded dragons, Pogona vitticeps, and Komodo dragons, Varanus komodoensis. For the former, it is more of academic interest versus practical relevance, while with the latter, most private practitioners should not be involved with that species. There are prominent veins in the roof of the mouth of most large boids. Earlier literature suggests these vessels as an option for phlebotomy, but the author has been unable to collect enough blood from these vessels for testing, not to mention the challenges of safety and ability to restrain the snake while the small vein is entered and collected from. Reptiles have taste buds on their tongue and oral epithelium. Tactile papillae are found along the head and oral cavity in some species. Tactile papillae along the head and oral cavity of some species, as well as olfaction, play a major role in courtship in snakes and lizards. All reptiles have an accessory olfactory organ called Jacobson's organ. Jacobson's organ is most highly developed in snakes where they receive data from the tip of the tongue as it flickers in and out. Chelonians only have a modified Jacobson's organ and it disappears in crocodilians during embryonic development.² Crocodilians have a velum palate or gular valve that can completely seal the mouth from the glottis and esophagus. This allows the crocodilian to sit in the water with its mouth open; however, for the veterinarian, there is a challenge to intubate and to visualize down the esophagus. In large boid snakes, there are visible pockets of lymphoid tissue/tonsils that have been a location to biopsy for a diagnosis of inclusion body disease; however, the author has had challenges in visualizing this tissue personally. The structure that many laypersons associate with the reptile, at least squamates (snakes and lizards), is the tongue. From dry, long, sheathed, and forked in the snake to yellow and fleshy in the bearded dragon to the amazing structure that is the chameleon tongue, perhaps no other organ epitomizes what people love or fear about reptiles.

Normal versus Abnormal

In close proximity to the oral cavity, are a host of other glands. Many chelonians have a single mental gland on their chin, that when fully developed, can confuse individuals into thinking it is an abscess that needs to be lanced or removed. In chameleons, bilateral glands in the lateral commissures of the mouth exude a greenish material that may be used for intraspecies communication, attraction of prey, or some other unknown function. Aggressive management of this site can lead to a spiraling downward trend of likely pain and anorexia in the chameleon. However in some cases, abscessation or impaction can be issues in these glands and need to be addressed medically, and in some cases environmentally. An anorectic bearded dragon may have a component of hepatic lipidosis; however, the yellow color to the tongue is normal. One may also misinterpret the "paleness" of a reptile's tongue as indicating anemia, while in fact it is always pale or shifts depending on environmental temperature/activity level. This also is reflected when the tip of the tongue of many lizard species becomes very red and inflamed from stress/handling. To the owner, this may appear as if the tongue was bitten or has pathology. Western hognose snakes, Heterodon nasicus, have a natural behavior, where they can spontaneously rupture capillaries in the mouth as part of their "play dead" mechanism. The author has experienced this while trying to gently open the mouth of an unhappy pet hognose snake with a cotton-tipped applicator, only to have the mouth suddenly fill with blood. Without knowing of this mechanism, one could assume there was pathology or iatrogenic trauma induced by the veterinarian. Many desert tortoise species will hypersalivate to manage overheating. While this may be normal physiology in the wild, it may indicate enclosure issues in captivity. Chelonians also may appear to have issues with their nasolacrimal duct (which in other reptiles enters the oral cavity in close proximity to the Jacobson's organ) because of the presence of epiphora; but this is normal because chelonians lack a nasolacrimal duct. Open-mouth breathing in a snake may not indicate respiratory, gastrointestinal, or oral pathology, but instead retained shed over/in the nares. Open-mouth breathing by a tortoise may simply reflect a desire to "taste" particles in the air using gular breathing to get those particles to the Jacobson's organ. Open-mouth breathing in lizard species may reflect a desire to cool their head/brain while still keeping their body in the desired temperature range while basking.

Oral Diseases

The list of oral diseases can be long. Cheilitis, stomatitis, osteomyelitis, periodontal disease (especially acrodonts), and abscesses are all fairly common bacterial, fungal, parasitic, or viral presentations. Of particular note are herpesviruses in numerous reptiles and iridovirus in chelonians. Copious tracheal mucus may reveal Strongyloides eggs or larvae from the lungs on a direct or stained smear. Facial abscesses may be secondary to trauma from the reptile hitting glass repeatedly. A simple solution of a solid dark barrier-like construction paper on the outside may be needed to address the primary issue. Nutritional secondary hyperparathyroidism (NSHPT) may present similar to an abscess due to callusing of fractures. Other nutritional concerns that may lead to oral presentations include hypovitaminosis A in chelonians and hypovitaminosis C in boid snakes.¹ Severe cases of NSHPT, congenital deformities, and facial trauma may permanently disfigure the skull and soft tissue, leading to chronic secondary cheilitis, stomatitis because of mucous membrane exposure. Foreign bodies lodged in the mouth or string foreign bodies wrapped around tongue or glottis may occur also. Numerous oral neoplasias have been reported.

Treatments, Procedures, Oral Surgery

Orally medicating reptiles can be a challenge in and of itself. Some animals, such as tortoises and Uromastyx, are extremely difficult to get the mouth open regularly and an esophageal feeding tube may be a reality. Some semi-aquatic turtles and lizards may open their mouth to bite or threaten, allowing an opportunity to pass a feeding tube or to inject a small amount of fluid. Reptiles that do not normally eat liquids may be challenged by the sudden presence of a moderate quantity of food/fluid in the back of the throat. With smaller quantities, the lizard can be held upright with the head tilted slightly to one side and gently drip the meds into the gap between lips. Most reptiles are best left to self-clear their oral cavity by swallowing or regurgitating if there is too much. They tend to keep their glottis closed when there is material present in the area and can hold their breath for a fair bit of time. Most aspiration that I have seen involved the person trying to clean the mouth out and continuing to handle and stress the reptile out. Crocodilians usually require a bite block and passing a tube past the gular region blindly. For snakes, one can easily pass a red rubber catheter of appropriate size directly into the philtrum that the tongue comes out, without needing to force the oral cavity open. Hiding food inside invertebrates/vertebrate prey, or items like cherry tomatoes for larger tortoises may be effective but volume may limit feasibility.

Oral and aural abscesses (these latter ones often have migrated up the eustachian tubes from the oral cavity) are best addressed by lancing and removing all of the inspissated pus. Often the inflammatory granulation tissue around these abscesses can be quite vascular and even thick until the often green-pea-looking pus is located. Generally, simple abscesses, once lanced and flushed, do not seem to need antibiotics in many reptiles. Multisite abscesses or ones that do not allow for complete removal and flushing do seem to improve with systemic antibiotics. Remember if wanting to culture these sites to not culture pus, but instead a piece of capsule and that ~ 50% of oral organisms in reptile mouths are anaerobic organisms.

Jaw fractures in reptiles may be best stabilized with suture/wire as cerclage, creative/lightweight KE apparatus, or wiring jaw shut with esophageal feeding tube. Chameleon tongue injuries may necessitate replacement under anesthesia, amputation and ligation, or euthanasia. There are reports of chameleons surviving without a tongue, but most do poorly. There has been one report of reattachment of a tongue.

Knowing dental type is important in approaching extraction versus salvage of teeth. For chelonians overgrown beaks, both rhinothecal and gnathothecal aspects, can present. While trims may be able to be performed awake, often general anesthesia/sedation can help. The author prefers to use alfaxalone at 10 mg/kg IM or IV to sedate for trims for smaller chelonians, still using a bite block. In most cases if given in a warmed enclosure, the animal is sedate in several minutes (1–20 minutes depending on several factors) and often ready to leave 1–2 hours post-injection. Mandibular prognathism may require a polymethylmethacrylate extension on the rhinotheca to pull it out over the gnathotheca as in birds, and an esophageal feeding tube placed.

Removal of venom glands in reptiles is controversial ethically and liability-wise. Some venomous reptiles may regrow the glands or have accessory glands. Generally, this procedure should only be performed by an experienced individual. In one instance, the author was contacted by a facility that trained seeing-eye dogs for the blind and wanted to expose them to the sounds, scent, and movements of a rattlesnake without putting the dogs at risk.

References

1.  Mehler SJ, Bennett RA. Oral, dental, and beak disorders of reptiles. Vet Clin North Am Exot Anim Pract. 2003;6:477–503.

2.  O'Malley B. General anatomy and physiology of reptiles. In: O'Malley B, ed. Clinical Anatomy and Physiology of Exotic Species. Philadelphia, PA: Elsevier; 2005: 17–93.