- Lizards lack tooth sockets or alveoli and their dentition is acrodont or pleurodont.
- Acrodont dentition is superficially attached to the biting edges of the mandible and maxilla.
- It is particularly important to take care when handling reptiles with acrodont dentition as the teeth will not be replaced.
- Chameleons and agamid lizards, such as bearded dragons and water dragons, possess acrodont dentition.
- Acrodont teeth are easily lost and are not replaced. Instead as teeth wear, the biting surface eventually becomes the bone itself.
- Pleurodont dentition is found in snakes and many lizard species, including iguanid lizards and monitors.
- With pleurodont dentition, a larger surface area of the tooth is in contact with the jawbone creating a stronger attachment.
- Pleurodont dentition is regularly replaced throughout life.
- Periodontal disease is particularly common in agamid lizards and chameleons. Owners often do not recognize any dental problems until disease is quite advanced.
One of the primary differences between reptiles and mammals is the structure and replacement of teeth. Repeated replacement of teeth or polyphyodonty is essential in many reptiles and there are many reasons for this strategy. First, the jaw is relatively small at hatch and must increase many-fold before maturity requiring multiple sets of teeth. The simple structure of reptilian teeth can also benefit from frequent replacement to maintain proper shape and sharpness of the dental crown. Most importantly, dentition is loosely attached to underlying bone in many reptiles, and teeth are easily lost during feeding or capture of prey. This superficial dental attachment is most pronounced in agamid lizards and chameleons, which creates special considerations during restraint and handling (Klaphake 2015, O’Malley 2005, Cooper et al 1970, Edmund 1970).
Terminology is central to any discussion of dental anatomy. Visit the glossary for definition of select dental anatomy terms.
Types of dentition
Like mammals, reptile teeth are composed of enamel, dentin, and cementum. Mammals possess heterodont dentition with four functionally different types of teeth: incisors, canines, premolars, and molars. Most vertebrates, including most reptiles, have homodont dentition. All teeth have the same shape, although they can differ in size. One exception to this homodontic rule of thumb is agamids, which possess more than one tooth type (Klaphake 2015, Phulari 2014, O’Malley 2005, Mehler 2003).
Three classical types of dental attachment have been described in the modern reptile: acrodont, pleurodont, and thecodont (Fig 1) (Table 1). The degree to which the teeth are attached to the wall and to the lingual shelf varies greatly between species, between upper and lower dentitions in the same species, and even along the length of a single jaw (Edmund 1970).
|Table 1. Types of dentition in reptiles (Klaphake 2015, O’Malley 2005, Chandra, McCracken 1999, Edmund 1970)|
|Site of attachment||Crest of bone||Inner side of mandible||Deep, bony socket|
|Strength of attachment||Superficial|
Teeth are easily lost
|Seen in…||Agamid lizards|
|Many lizards, including iguanids, monitors||Crocodilians
Snakes (modified thecodont)
|Replacement||Teeth are not replaced||Teeth are constantly shed and replaced throughout life||Frequency and speed of replacement decreases as animal ages
CLINICAL TIP: When managing an infected or fractured tooth in a reptile, it is important to know the dental type for your species of interest. Is the most appropriate approach extraction or salvage, because there will be no replacement tooth? (Klaphake 2015).
Acrodont teeth are seen in agamid lizards (e.g. water dragon, bearded dragon), uromastyx, chameleons, and tuataras (Table 1). Acrodont teeth are superficially ankylosed to the rim of shallow, crater-like depressions on tooth-bearing bone (Fig 1). This attachment is relatively weak and teeth are easily lost while feeding or capturing prey (Klaphake 2015 O’Malley 2005, Mehler 2003, Cooper et al 1970, Edmund 1970).
As the animal grows, new teeth can be added at the posterior end of the tooth row, however acrodont teeth are replaced “only very rarely” in the adult. Instead teeth are worn down with age leaving only the dorsal crest of the mandible and the ventral crest of the maxilla. The resultant cutting edge in older animals is similar to the chelonian jaw, except the surface remains serrated. Glancing contact between the occlusal surfaces when the jaws close, ensures wear maintains a sharp edge (O’Malley 2005, Mehler 2003, McCracken 1999, Cooper et al 1970, Edmund 1970).
CLINICAL TIP: Take special care when handling species with acrodontic dentition as the teeth will not be replaced if damaged or broken (Diaz-Figueroa 2006).
Pleurodont teeth are seen in snakes, many lizards, including iguanids, varanids (monitors), basilisks, chuckwallas, and anoles (Table 1) (Klaphake 2015, Edmund 1970). With pleurodont dentition, a larger surface area is in contact with the jawbone, which creates a stronger attachment than acrodont dentition (Fig 1).
Pleurodont teeth are constantly shed and replaced throughout life. The lifespan of teeth varies along the jaws, with posterior teeth lasting longer than anterior teeth. Most teeth last only a few months before being shed and ingested with prey during feeding (Cooper et al 1970, Edmund 1970).
As each tooth completes its life cycle, the bone of attachment is actively formed and resorbed. A new tooth sits in reserve in pits within the gum lingual to the old tooth. Tooth replacement does not appear to occur in response to wear or injury of individual teeth. Instead each tooth is replaced as part of a regular wave-like pattern affecting the entire dental arcade (Klaphake 2015, O’Malley 2005, Edmund 1970).
Boids, pythonids, and colubrids (e.g. corn snake) display a back-to-front progression of alternating waves. Some venomous snakes, like viperids and crotalids, tend to display simple alternate replacement, while in elapids, such as the cobra and coral snake, replacement waves progress from front to back. This replacement rhythm may or may not be synchronous on both sides of the mouth. If synchrony is present, it usually manifests only on the premaxilla (Edmund 1970).
The thecodont tooth has a relatively long cylindrical base set in a deep bony socket (Fig 1). All mammals exhibit thecodonty, however crocodilians are the only living reptiles with thecodont dentition (Table 1). Thecodont teeth have deep attachments, allowing teeth to withstand strong forces. Lost teeth can be replaced by a limited number of replacement teeth in crocodilians, however the frequency and speed of replacement decreases as the animal ages (O’Malley 2005, Mehler 2003, Edmund 1970).
Traditionally, snake dentition has been described as pleurodont, however snake teeth have more recently been described as modified thecodont because each tooth is fused to the rim of a shallow socket (Jacobson 2007, Edmund 1970).
Unlike snakes and chelonians, many lizards chew their food and tear off pieces when food items are too large to swallow. Lizards usually have sharp, tricuspid or cone-shaped dentition (Fig 2). The number of teeth in the dental arcade is usually greater in the adult than in the young (O’Malley 2005, Mehler 2003, Edmund 1970).
Tuataras, chameleons, and agamid lizards, like water dragons and bearded dragons, are the only species that have true acrodont dentition. Acrodont teeth are weakly attached and lost relatively easily while feeding or capturing prey. With the exception of chameleons, most acrodontic species also have a number of conical pleurodont teeth in the rostral-most portion of the upper and lower jaws. The crowns of these pleurodont teeth are long with sharp points curved inwards and backwards. Among the living reptiles, these two distinct types of dentition are a rare example of marked heterodonty (Klaphake 2015, O’Malley 2005, Mehler 2003, McCracken 1999, Cooper et al 1970, Edmund 1970).
In chameleons, the premaxilla is quite reduced with fewer teeth in this rostral location (Fig 3) (Edmund 1970).
In family Agamidae these acrodont teeth are broad-based, somewhat laterally compressed, and triangular in profile. The crowns of herbivorous agamid Uromastyx spp. show no division into cusps but are chisel-shaped and extremely sharp at their working edges. In adult uromastyx, the two anterior teeth in each maxilla and dentary bone and four teeth on the premaxilla are worn to such an extent that a continuous cutting edge is created. This biting plate is used to cut and tear plant material (Diaz-Figueroa 2006, Cooper et al 1970, Edmund 1970).
CLINICAL TIP: Periodontal disease is common in lizards with acrodont dentition in captivity but not in the wild (Wellehan 2014, Mehler 2006).
Pleurodont teeth are found in many lizards, including all iguanids, all varanid lizards, as well as members of family Gekkonidae. These teeth tend to be isodont, or approximately the same size and form (Klaphake 2015, Mehler 2003, Edmund 1970).
In many lizards, especially family Iguanidae, the typical tooth is cylindrical, sometimes slightly constricted below the crown, and often compressed laterally and expanded anteroposteriorly to create a sharp, serrated cutting edge, suitable for chopping leaves (Fig 4). Palatal teeth occur in some genera, but these teeth are always small and never very numerous. In the iguana, each quadrant contains approximately 20-30 teeth. Rapid tooth replacement appears to be the rule in iguanids. Each tooth may be replaced five times a year and as many as four teeth per year may be added to the posterior end of the tooth row in rapidly growing animals (Edmund 1970).
In monitors, the teeth have broadly flaring bases and in most species the teeth are conical, relatively short, laterally compressed, and cultriform (knife-life, with fairly sharp tips) (Fig 5). The teeth increase in size toward the rear of the jaw. In most species, there are one or two replacement teeth at each position, but the Komodo dragon (Varanus komodoensis) may have as many as four or five (Edmund 1970).
Some lizard species that utilize unique dental strategies. The caiman lizard (Dracaena guianensis) and adult Nile monitor (Varanus niloticus) feed upon hard-shelled prey, like snails and clams, and they possess incredibly strong jaws and specialized molariform teeth. The cheek teeth are small, flat, broad, and bead-like with crowns that have expanded to form broad crushing or grinding surfaces (Fig 6). Interestingly, the cheek teeth of the Nile monitor are conical and sharp during much of its life, but when the animal reaches maturity and its nutritional strategy changes to durophagy, or a molluscivorous diet, the teeth become broad and biscuit-shaped (D’Amore 2015, Edmund 1970).
The Gila monster (Heloderma suspectum) and Mexican beaded lizard (Heloderma horridum) possess venom glands in the lower jaw. Venom is delivered through unique grooved mandibular teeth as the helodermatid chews on its prey. Each groove is flanked by a cutting flange, which makes the tooth better adapted for piercing flesh (Fig 7) (Clayton 2014, Beck 2005, Ast 2003).
Suborder Ophidia swallow prey whole, therefore snake teeth are primarily designed for holding prey and not chewing. In most species, the teeth are long, thin, and curved backwards to prevent escape (Fig 8) (O’Malley 2005, Edmund 1970).
CLINICAL TIP: If a snake bites and attaches to a human, simply pulling the snake free can tear the skin. Gently extract the snake by pushing the head forward to “unlock” the teeth (Diaz-Figueroa 2006).
Snakes have modified thecodont dentition. The arrangement and number of teeth varies. Some species have almost no teeth and others have many, highly developed teeth. In all colubrids the premaxilla is toothless, but teeth are usually well developed on the dentary bone and in a long row on the palatine and pterygoid bones. Most boids and pythonids possess a moderately large number of teeth on all bones. Most snakes seen in clinical practice have two mandibular rows of teeth and four maxillary rows (Fig 9) (Clayton 2014, Finch 2010, O’Malley 2005, Mehler 2003, Edmund 1970).
Although many snakes are aglyphous or “fang-less”, some species possess specialized, cone-shaped, tapered maxillary teeth or fangs, which inject venom into prey. Venom is transported to the base of the fangs from modified salivary glands or postorbital venom glands. Venomous species can be classified based on their venom delivery system (Durso 2013, O’Malley 2005, Edmund 1970).
Proteroglyphous snakes possess simple fangs connected by a venom duct to large glands in the temporal region of the head. Short, hollow fangs sit at the front of the maxilla and remain erect when the mouth is closed. Proteroglyph or “fix-fanged” snakes include elapids, such as cobras, mambas, death adders, and coral snakes. These species typically strike their prey and then hang on until venom has taken effect. Some elapids also constrict and envenomate their prey at the same time (Johnson 2010, O’Malley 2005, Mehler 2003).
The fangs of opisthoglyphous species sit at the end of the maxillary tooth row at the rear of the mouth. Venom travels along a simple groove on the back of the tooth to the tip of the fang. One or two grooved fangs are found in several groups of colubrids, including hognose and vine snakes. These species typically must chew on prey to bring the fangs into a biting position (Durso 2013).
As a general rule, bites by most “rear-fanged” snakes are not particularly harmful to humans, causing relatively mild, transient, local symptoms. Exceptions to this rule of thumb include two members of subfamily Colubrinae: boomslangs (Dispholidus typus) and twig snakes (genus Thelotornis). Bites from these species have caused several human fatalities because the fangs are larger, relatively close to the front of the mouth, and their venom is quite potent (Durso 2013).
In members of family Viperidae (vipers and pit vipers such as rattlesnakes), the maxilla bears a single, highly modified fang. This long, tubular or needle-like fang has a hollow core (Fig 10). Venom is injected from a slit-like opening near, but not at, the tip of the fang. The fangs are so long that when the mouth is closed these specialized teeth fold back into a sheath along the roof of the mouth covered by a membranous flap (Fig 11) (Durso 2013, O’Malley 2005, Mehler 2003).
Fangs are shed regularly to be replaced by reserve teeth. Vipers shed their fangs approximately every 2 months (Durso 2013, O’Malley 2005).
For additional information on fangs and venom delivery systems, go to Snake Venoms and Envenomation by Sherman Minton or visit “Life is Short, but Snakes are Long”
All crocodilians possess thecodont dentition. The teeth are used to grasp prey, but not chew, as most prey is swallowed whole after being tossed into the back of the pharynx. Larger prey is torn apart by firmly grasping the food item with teeth while shaking the head from side to side or rolling the entire body. Teeth are conical in shape and arranged in two rows in many crocodilians (Fig 12). Teeth are replaced throughout life however the number of replacements is limited and slows with age (Mehler 2003, Edmund 1970).
CLINICAL TIP: The replacement tooth can initially come in at a strange angle in crocodilians, however the tooth generally straightens after a short period of time (Klaphake 2015).
There are differences between the anatomy of the maxillary and mandibular bones in crocodiles and alligators that can affect the visual examination (Mehler 2003). For example, the alligator maxilla is wider than the mandible creating an overbite (Fig 13).
|Upper jaw is wider than the lower jaw causing an overbite||Upper and lower jaw are approximately the same width|
Additionally, crocodiles can be differentiated from alligators and caimans by a fourth mandibular tooth that is visible on each side of the mouth when the mouth is closed (Fig 14) (Mehler 2003).
|The large fourth mandibular tooth fits into a socket in the upper jaw and cannot be observed when the snout is closed||The fourth mandibular tooth projects outside the snout when the mouth is closed|
Chelonians have no teeth. Like birds, teeth have been replaced by a keratinized horny beak or rhamphotheca, which overlies the bone (Fig 15). Most chelonians depend on the scissor-like action of the rhamphotheca for prehension and cutting food, which is then swallowed whole. Snapping turtles also possess extremely sharp cutting edges or tomia on the beak. Chelonians will also rip off pieces of food by retracting their neck muscles. Captive chelonians have been observed putting a foot on food items before pulling back. Some species possess a pronounced, rostrally located secondary palate or crushing plate and most herbivorous species also have a row of tough chewing ridges on the palate to allow more precise chewing of fibrous food items (Klaphake 2015, Clayton 2014, Chitty 2013, Boyer 2006, O’Malley 2005, Mehler 2003).
Most newly hatched oviparous squamates (snakes and lizards) have a functional egg tooth (Fig 16). This highly modified premaxillary tooth serves to rupture the embryonic membranes and eggshell during hatch. Many geckos have a double egg tooth or an egg tooth at the mesial (anterior) margin of each premaxilla. Viviparous squamates generally show marked reduction of the egg tooth. The egg tooth is lost during the first few days of life or after the first shed. There is often a midline tooth, which may be the successor to the egg tooth (O’Malley 2005, Mehler 2003, Edmund 1970).
In chelonians, crocodilians, and tuatara the analogous structure is the egg caruncle, a horny epidermal point which bears no relation to true dentition (Fig 17) (Edmund 1970).
Examine the mouth for evidence of fractured teeth, cheilitis, periodontal disease, and stomatitis. Evaluation of the oral cavity can be safely accomplished for most reptiles commonly seen in clinical practice, however some species must be examined under sedation or general anesthesia because they are venomous or can cause serious damage with their powerful bites and razor-sharp teeth. Clayton (2014) recommends midazolam (0.3–1.0 mg/kg intranasal, IM, or SC) with sedative effects observed within 10–20 minutes. Venomous species should only be evaluated by experienced individuals and only after clinic liability coverage has been confirmed (Clayton 2014, Mehler 2003).
CLINICAL TIP: Reptiles typically object to manipulation of the mouth so leave evaluation of the oral cavity until the end of the physical exam (Finch 2010, Mehler 2003)
Many reptiles will gape when restrained so use this opportunity to get a cursory look at the mouth. Fortunately, squamates have a kinetic joint between the maxillary jaw and skull, which allows a relatively wide mouth gape (Fig 18) (Clayton 2014, O’Malley 2005).
Although lizards have a large gape, the fused mandibular symphysis means they cannot open their mouths as widely as snakes. Lizards compensate by having stronger jaws with extremely strong adductor muscles (O’Malley 2005).
CLINICAL TIP: Always use a mouth gag when examining the mouths of large healthy lizards as the jaw can close like a trapdoor causing considerable pain and injury (O’Malley 2005)
OPENING THE MOUTH
A quick evaluation of lizard teeth can be performed by gently grasping the dewlap in species like the iguana and bearded dragon (Fig 19, Fig 20). Mehler (2003) recommends applying gentle pressure to the eyes with one hand, to stimulate the vagal–vagal response, and gently pulling the dewlap down with the other hand. For a more stubborn lizard, applying gentle pressure to the lateral aspects of the mandible and maxilla will often cause the mouth to open (Mehler 2003).
After the mouth is open, a more detailed exam can be performed using an oral speculum. Many items can serve as mouth gags, such as soft, plastic spatulas or hemostats of appropriate size padded with porous tape or elastic bandage material (Table 2). Hotel room key cards can work well in smaller lizards and are disposable (E. Klaphake, personal communication, February 27, 2018). Metal specula can be used, but use caution to avoid causing trauma to the mouth (Mehler 2003).
|Table 2. Oral specula commonly used in lizards and snakes (Clayton 2014, Mehler 2003)|
Teeth and oral soft tissue structures can be damaged by inappropriate handling technique, particularly in animals with acrodont teeth. Occasional breakage or tooth loss is not an issue with pleurodont dentition (Clayton 2014).
Visit LafeberVet’s Lizard Handling and Restraint for additional information and safety tips.
There are no teeth in the rostral aspect of the snake mouth. To open the mouth, gently introduce the oral speculum on midline. As the mouth opens, advance the speculum further until a thorough evaluation can be performed (Fig 21). The wide gape found in squamates is most pronounced in snakes because of a mobile mandibular symphysis and loose attachments between the quadrate bone and the rest of the skull (Clayton 2014, Mehler 2003).
CLINICAL TIP: A light, gentle touch is necessary to evaluate snake teeth.
Visit Snake Handling and Restraint for additional information and safety tips.
Gently tapping the nose can often elicit a gape response in the crocodilian, however evaluation of the teeth often requires experienced handlers and heavy manual restraint.
In turtles and tortoises, the maxillary-skull joint is akinetic and the gape is relatively narrow when compared to snakes and lizards. Depending on the species and your patient’s health status, the oral exam can be incredibly challenging in the chelonian. Large, uncooperative, and more dangerous chelonians require anesthesia for a thorough oral exam (Clayton 2014). Visit Chelonian Handling and Restraint for detailed information.
Primary and secondary oral disease is common in reptiles. Periodontal disease is a significant cause of morbidity in captive agamid lizards and chameleons (Fig 22). Important underlying causes of disease in captive animals include infection, inappropriate nutrition, and trauma. Chronic trauma, like hitting glass, or secondary hyperparathyroidism are frequently associated with facial deformities that can cause improper alignment and exposure or irritation of tissues. When soft foods are regularly fed to captive lizards, these food items can accumulate around tooth roots promoting the formation of plaque. As plaque builds up on teeth, bacteria begin to colonize and a reversible inflammatory response develops within marginal gingiva leading to periodontal disease. Gram-positive aerobic cocci predominate in reptiles with excessive plaque buildup. As plaque matures, anaerobes, Gram-negative bacteria, and spirochetes are seen (Clayton 2014, Mehler 2006, Mehler 2003, McCracken 1999).
CLINICAL TIP: Feeding a natural diet provides the required texture and consistency to prevent dental plaque from developing (Mehler 2006, Mehler 2003).
Clinical signs of dental disease include gingival erythema and dental calculus. As periodontal disease progresses and calculus builds, gingiva first becomes swollen and gingival margins begin to recede, exposing underlying mandibular and maxillary bone. In advanced disease, the gingiva becomes hyperplastic and gingival pockets form. Suppurative gingivitis, subcutaneous abscessation, and focal or multifocal osteomyelitis can develop. In the most severe cases of periodontal disease, pathologic fractures occur as well as fatal systemic infections (Table 3) (Mehler 2003, McCracken 1999).
|Table 3. Clinical signs of dental disease in lizards (Mehler 2006, Mehler 2003)|
CLINICAL TIP: Many reptiles often continue to eat with early dental disease. Plaque formation and gingival erythema are usually only recognized during oral examination. The owner may not detect a problem until disease is quite advanced (Clayton 2014, Mehler 2003).
Management of periodontal disease in lizards should begin with a thorough oral exam under general anesthesia. The goals of dental care in lizards are the same as for other taxa. After calculus is removed and gingival sulci are cleaned under general anesthesia, the oral cavity is irrigated with 0.05% chlorhexidine solution. Systemic antibiotics are often indicated as well. To prevent the development or progression of disease, dental cleaning should be performed every 6-12 months (Mehler 2006, Mehler 2003).
Reptile teeth tend to be relatively uniform with a simple, conical shape and most reptile teeth are loosely attached with the dental attachment most superficial in acrodontic species. Tooth loss and replacement is a normal occurrence in reptile species with pleurodont dentition, which includes snakes, and many lizards. Take special care when handling reptiles with acrodont dentition as teeth will not be replaced when infected or fractured. Additionally, periodontal disease is common in captive lizards with acrodont dentition such as bearded dragons and chameleons. Periodontal disease is an insidious condition. As plaque formation builds and gingivitis worsens, many reptiles will continue to eat. The owner may not observe problems until disease is quite advanced. Feeding lizards an unnatural, soft diet is believed to promote plaque development and the development of periodontal disease.
- Acrodont: dentition attached to crest of bone, present in some lizards (e.g. agamids, chameleons)
- Aglyphous: “fang-less” snake with undifferentiated teeth
- Apex: root or basal portion of a tooth
- Cement, cementum: a thin layer of specialized calcified material that covers the base of the tooth and fixes the tooth to the jaw
- Cultriform: knife-life or fairly sharp tips (e.g. family Varanidae)
- Denticulate: having small teeth or toothlike projections; finely toothed (e.g. family Iguanidae)
- Dentin: hard, dense, bony tissue forming the bulk of a tooth beneath the enamel
- Distal: Per Edmund 1970, this term is preferred to “anterior” because of the curved shape of the dental arcade
- Enamel: mineralized surface of the tooth
- Heterodont dentition occurs (primarily) in mammals in which there are four functionally different types of teeth: incisors, canines, premolars and molars
- Homodont dentition is found in the majority of vertebrates including reptiles in which all teeth are functionally and anatomically the same type, although their size can vary depending on location
- Isodont dentition is another term for homodonty
- Labial: The side of a tooth that is adjacent to (or the direction towards) the inside of the lip (labium); the term ‘buccal’ is usually reserved for mammals
- Lingual: the side of a tooth adjacent to (or facing) the tongue
- Mesial: directed towards the midline of the body; preferred to “posterior” because of the curved shape of the dental arcade
- Occlusal: crown or tip of a tooth
- Opisthoglyphous: rear-fanged venomous snake
- Pleurodont dentition attach to labial wall; present in snakes, some lizards; regularly replaced throughout life
- Polyphyodont dentition involves replacement of teeth over several times in a lifetime so that the jaws are never left without teeth
- Premaxilla: the teeth-bearing bone at the front of the upper jaw
- Proteroglyphous: venomous “fixed-fanged” snakes with simple, relatively short fangs that are constantly erect
- Root: The term does not apply to any known reptile; “base” or “apex” is more appropriate
- Solenoglyphous: venomous snakes possessing long, tubular or needle-like fangs that collapse into a membranous sheath when the mouth is closed
- Thecodont: dentition attached to jaw securely in deep bony socket
Thank you to Dr. Javier Nevarez for helpful feedback and recommendations during early development of this manuscript.