Koalas feed exclusively on a fibrous, abrasive diet of Eucalyptus spp. foliage. Selective digesta retention in the cecum allows them to feed on leaf with poor nutritive value.1 Efficient digestion of this material also relies on specialized dental morphology. Koalas possess high, tightly interlocking molar cusps, with opposing long, curved blades—producing an efficient cutting-shearing action.2 The influence of age-related dental wear on digestive efficiency of koalas and, therefore, their longevity, is well understood;3,4 however, dental malocclusion is now recognised as a frequent finding in captive and free-ranging koalas in Queensland5 and South Australia (Pettett, unpublished data).
Since 2007, dental disease has been recognised as a significant cause of morbidity and mortality in the Melbourne Zoo koala collection. Dental malocclusion is now understood to be the primary cause of abnormal dental wear in these cases. Most frequently, upper incisor wear results in pulp exposure and tooth root abscess.
When dental abnormalities are detected, CT scanning is used to identify any osteolytic lesions. Dental extraction plus local antimicrobial therapy (prolonged-release antibiotic copolymer or antibiotic-impregnated polymethylmethacrylate beads) has been the chosen therapeutic approach. However, the prognosis for recovery remains poor. Complications that have developed during treatment include nasolacrimal duct dysfunction, progressive osteomyelitis, severe facial cellulitis, aspiration pneumonia, and gastrointestinal disease. In 2018, Melbourne Zoo veterinarians conducted a population health assessment in free-ranging koalas at Framlingham Forest, VIC, Australia, and identified dental malocclusion in 34 of 162 koalas examined.
1. Cork SJ, Warner ACI. The passage of digesta markers through the gut of a folivorous marsupial, the koala (Phascolarctos cinereus). J Comp Physiol B. 1983;152(1):43–51.
2. Lanyon JM, Sanson JD. Koala (Phascolarctos cinereus) dentition and nutrition. I. Morphology and occlusion of cheekteeth. J Zool. 1986a;209(2):155–168.
3. Lanyon JM, Sanson JD. Koala (Phascolarctos cinereus) dentition and nutrition. II. Implications of tooth wear in nutrition. J Zool. 1986b;209(2):169–181.
4. Logan M, Sanson GD. The effects of tooth wear on the activity patterns of free-ranging koalas (Phascolarctos cinereus Goldfuss). Aust J Zool. 2002;50(3):281–292.
5. Pettett LM, McKinnon AJ, Wilson G, Carrick FN. The development of an oral health charting system for koalas (Phascolarctos cinereus). J Vet Dent. 2012;29(4):232–241.