The dentition of myomorphs is characterized by the formula I 1/1, C 0/0, PM 0/0, M 3/3, for a total of 16 teeth with a marked dental diastema (Fig. 1). Unlike rabbits, taken as an example, in myoporphs only the incisors have a "continued growth", thanks to the presence of open roots (Fig. 2). Consequently, in the mouse and in the rat, abnormal teeth growth occurs only in the incisors. In the adult rat, the yellow-orange colour of the incisors is perfectly normal and is due to iron deposition in the enamel (Fig. 3).
Among the most frequent causes of malocclusion are congenital defects, teeth or mandibular fractures and a possible inappropriate diet in terms of food texture (Fig. 4). In the presence of malocclusion, the lower incisors typically suffer a deviation that makes them grow outward (Fig. 5), often at a marked angle; conversely, the upper incisors tend to "curl" inward or to deviate laterally. The contact between the deviated tooth’s cutting edge and the oral mucosa may be the cause of different injuries, from simple ulcers to perforation of the tongue, cheeks and hard palate; in view of the “mechanical” impairment or of the pain caused by such lesions, that tend to get infected by common oral bacteria, food intake or chewing are compromised. Hypersalivation, anorexia and weight loss are the most obvious consequences secondary to the altered structure of the incisors and to the lesions of the oral mucosa.
The teeth of myomorphs should undergo periodic trimming, approximately every 4-6 weeks. The trimming, performed with a pair of nippers, must be carried out prudently as it can result in the formation of spikes or sharp edges that can injure the tongue or, in the long run, result in longitudinal fractures of the teeth. Alternatively, a dental bur may be used, after sedation of the animal.
As for the eventual extraction technique, which is routinely used in rabbits with malocclusion, we report verbatim Hillyer and Queensberry (1997): "extraction of the incisors is an alternative to trimming; however, this procedure is difficult because of the incisors' long roots".
The presenceof intra-oral lesions should be treated using broad-spectrum antibiotics and, possibly, anti-inflammatory agents/pain relievers in order to allow the animal to return to eating as soon as possible.