Abstract

The warthog is a species within the Suidae family indigenous to the northern and southern African savanna plains. Warthogs differ from many of the Suidae in their dental formula. The formula of most Suidae is I:3/3, C:1/1, PM:4/4, M:3/3, while the warthog is described as I:0–1/3, C:1/1, PM:3/2, M:3/3.3 However, examination of an adult warthog’s dentition usually reveals a reduced number of teeth which will surprise the first-time observer. In addition, the structure of the molars, and in particular the third molar, is unique and has clinical implications for dental procedures.

There is a recently clarified species division in warthogs.⁷ If incisors are present in the maxilla, the species is considered to be the common warthog (Phacochoerrus africanus). Individuals that do not possess upper incisors, or have very small, or non-erupted incisors are considered to be the desert warthog (Phacochoerus aethiopicus) and is distributed in parts of Ethiopia, Somalia and Kenya. The desert warthog is also considered to be smaller in body size. Within the 2 species there are 6 subspecies divisions, however these show no apparent trends in dentition.

In addition to the species differences, the present study and others have documented a considerable individual variation in teeth numbers. In a study which examined over 1200 warthog skulls in Zimbabwe, the majority contained 2 premolars, some had 3 premolars and 1 single skull showed a first deciduous premolar. Thus, the dental formula of P. africanus is I:1–2/2–3, C:1/1, PM:2–4/1–2, M3/3 and that of P. aethiopicus is I:0/0–2, C:1/1, PM:2–3/1–2, M:3/3 (J.P. d’Huart, personal communication). Lastly a process of normal permanent teeth loss is apparent where by premolars and anterior molars are progressively lost as the third molar grows.¹ Examination of the oral cavity will reveal a spectrum of normal dental formulas and differences must not be viewed with alarm. In many very old animals the only teeth remaining were the canines and third molars giving a geriatric dental formal of I:0/0, C: 1/1, PM: 0/0, M:1/1.

At Ol Jogi, Ltd, Laikipia District, Kenya, 18 warthog maxillas and 9 mandibles were opportunistically collected and examined for their dental formula. All skulls showed distinct upper incisors identifying these warthogs in Laikipia as belonging to the P. africanus species. All skulls had complete permanent dentition indicating they were over 24-mo-old.¹

Anatomy of Premolars and Anterior Molars

The premolars and molars are generally squarish teeth that are composed of irregular shaped tubules of dentine bonded together by cement. The number of tubules that form each tooth varies between individuals. Tubules may be bifurcated and originate from common roots or individual tubules may have single roots. As teeth wear down the coalescing of tubules becomes noticeable. The number and structure of roots also varies between individuals and the process of dental change. As the third molar applies pressure to the anterior teeth roots become twisted, curved caudally, constricted and then disappear. Some teeth have virtually no roots at all and pulled away from the skull with a minimum of force.

Anatomy of the Third Molar

The third molar is composed of a large number of closely set cylinders of dentine embedded in cement of different sizes.⁵ M3 of the upper jaw has an average length of 44 mm, a width of 12 mm and a depth of 60 mm (n=12). Third molars of up to 70 mm in length have been recorded.¹ The tubules from the third molar curve slightly caudally. It has been considered the M3 is growing through most of the animal’s life. The first portion of the tooth to erupt forms the anterior edge and additional tubules continue to erupt at the posterior aspect of the tooth until well into adulthood.¹ Cutting the molar vertically and horizontally shows that the greater majority of dentine cylinders do not branch or fuse together into common roots. Each tubule has its own root. However, in the posterior aspects as many as 3–4 tubules may originate from common roots. Several molars were noted to have individually rooted tubules buried within a group of tubules with a common root.

Changing with Age

Growth over time of the third molar has been described.⁴ Continued eruption of tubules from the posterior aspect of the tooth causes forward movement of M3. As the premolars do not move, pressure is put against M1 and M2. This changes the teeth’s shape and their root’s direction eventually constricting the roots causing loss of contact with the socket and thus, loss of the tooth. Following, M3 applies pressure to the premolars which are in turn lost by a similar process.

Wearing of any tooth does not always follow from front to back. On 5 skulls, the first or second molar of the maxilla were completely worn down to a smooth surface, while their anterior neighbor, the 3rd PM or 1st molar, had not been worn down to such extent. The opposing tooth of the mandible was also worn down to the same extent so that when looking at the lateral surface of the skull a window like gap of 5–8 mm is seen. In addition, another abnormal wear pattern was noted on two skulls. In both of these a large hook extending 1 cm above the level of the molar ridge on one side was present. In one case the tooth was M3 on the mandible, the only remaining tooth and in the other the second molar of the maxilla which was still within the premolar/molar row.

Lastly incisors are also lost over time.¹ The process is not clear but appears due to wear over time. However, the loss of incisors does not seem to affect the animal’s ability to feed.

Possible Dental Procedures?

It will be important to determine the degree of bifurcation and the root pattern in a diseased molar. Use of endodontal probing and dental radiography, possibly with contrast fluids being injected into the root canal^2,6 will be of vital importance. If the radiographs show the root canal to be separated from the surrounding cylinders it might be possible to drill the single cylinder loose or to remove fractured remnants of cylinders. However, the length of the roots and their slight curve will make this procedure difficult and risky as the root or drill might fracture in the depths while working on it.

If more cylinders are involved in the disease process or a fracture is present, a split in the multi rooted molar for partial removal of the diseased area could be considered.⁶ Drill assistance will be needed. Cleaving of the tooth with a chisel will not be possible. While working on postmortem specimens it was noted that the cylinders do not break along the boundary lines but make jagged cuts through adjacent dentine and root cavities.

Total extraction of a molar may not be feasible in aged animals as the only remaining grinding teeth could be the third molars.¹ There should be great concern regarding the affect on the opposing tooth and the ability of the animal to masticate.

Any oral approach will be difficult due to limited access for instruments. A total extraction of the third molar will require a surgical approach through the buccal wall on the lateral surface, keeping in mind that the large masseter muscle will make access difficult. Osteotomy procedures will follow to gain access to the roots of the third molar.

Acknowledgments

We would like to thank the owners and management of Ol Jogi, Ltd for their support. The rangers and livestock herders deserve thanks for collecting samples. Special thanks to Mr. Muriithi J. Mugo, Ms. Hester van Bolhuis, and Ms. Nina Deibel.

Literature Cited

1.  Child G, Sowls L, Mitchell BL. 1965. Variations in the dentition, ageing criterion and growth patterns in wart hog. Arnoldia. 38(1): 1–23.

2.  Eisner ER. 1995, Performing surgical root canal therapy in dogs and cats. Vet Med. 90(7):648–661.

3.  Fowler ME, ed. 1993. Zoo and Wild Animal Medicine, 3rd ed. W.B. Saunders Co., Philadelphia, Pennsylvania.

4.  Middleton Shaw JC. 1940. Growth changes and variations in warthog third molars and their palaeontological importance. Trans Royal Soc. (S. Af.), 27:51–94.

5.  Nowak RM, Paradiso JL, eds. 1983. Walker’s Mammals of the World, 4th ed. The Johns Hopkins University Press, Baltimore and London.

6.  Smith MM. 1995. The clinical significance of root morphology in periodontal disease in dogs. Compend Contin Ed Pract Vet. 17(5):625–636.

7.  Vercammen P, Mason DR. 1993. The Warthogs (Phacochoerus africanus and P. aethiopicus). In: Pigs, Peccaries and Hippos. IUCN, Gland, Switzerland.