Dentistry of rabbits (Proceedings)


Dentistry of rabbits (Proceedings)

Apr 01, 2008

Dental disease is common in pet rabbits and can produce a wide range of clinical signs and symptoms. Underlying causes of dental disease are still subject to debate, but can be divided in congenital and acquired disease. Congenital dental disease is usually limited to malocclusion of incisors, especially in dwarf or brachycephalic breeds. Acquired dental disease can be related to nutrition (lack of wearing, metabolic bone disease), trauma or age-related attrition. Treatment of dental disease is designed to return anatomy and function as close to normal as possible, and to control associated infection and inflammation.

Normal dental anatomy and physiology

Proper diagnosis and treatment of dental disease requires a thorough understanding of normal rabbit dental anatomy and physiology. The rabbit has continually growing, open rooted (elodont) incisors and molars. Premolars and molars are anatomically indistinguishable, and are therefore simply termed "cheek teeth". There are two pairs of maxillary incisors, the second smaller incisors located behind the larger, easily visible incisors. These are commonly called "peg teeth". The normal dental formula of rabbits is I2/1 C0/0 P3/2 M3/3 for 28 teeth. When the jaw is at rest, the mandibular incisors rest between the first and second maxillary incisor teeth. Maxillary first incisors are shorter than the mandibular incisors, and have a central longitudinal groove on the labial aspect that is not present on the mandibular incisors. Normal grinding motions during chewing produce sufficient wear to keep incisors at the proper length in the normal animal. Normal molars have longitudinal grooves on the buccal aspect of each tooth, and the occlusal surfaces are flat, but not smooth. Irregular surfaces help in the crushing of hard, fibrous food. Similar to incisors, normal crushing of food produces adequate wearing of continually growing cheek teeth in the normal animal. There is no significant interproximal space between incisor or cheek teeth.

Pathophysiology of dental disease

Dental disease is a result of anatomical or physiologic abnormalities of incisor teeth, cheek teeth, or both. Any process interfering with normal eruption of or wearing of continuously growing teeth will result in dental disease. Disease of incisors can be secondary to primary disease of cheek teeth, and vice versa. For example, primary congenital malocclusion of incisors prevents proper wearing of the incisal edges of the teeth, and subsequent overgrowth. Elongation of incisors prevents proper occlusion of cheek teeth, with subsequent overgrowth and possible development of sharp points or spurs.

Insufficient wearing has been proposed as a leading cause of acquired dental disease. This theory is based on evidence that the diet of pet rabbits often significantly differs from that of their wild European counterparts, who consume rough grasses with higher silica content. Jaw movements of rabbits consuming rough hay have a significantly wider horizontal component than rabbits consuming a concentrated pelleted diet. This decreased horizontal jaw motion in pet rabbits eating pellets may result in decreased normal wear of continuously erupting teeth.

Any process that interferes with eruption of elodont teeth can potentially impact normal occlusion. Francis Harcourt-Brown has proposed metabolic bone disease (MBD) as a potential cause of acquired dental disease. Studies have demonstrated demineralization of skull bones, lower serum calcium and higher PTH levels in severely affected rabbits. MBD produces demineralization of bone matrix and subsequent changes in skull and teeth structure, interfering with normal occlusion and wearing of continuously growing teeth.

Table 1. Causes of dental disease.
Regardless of the initiating cause of abnormal wearing of elodont teeth, the result is elongation of crowns. Overgrown, elongated incisors may develop a number of abnormal growth patterns, including lateral deviation with or without subsequent damage to soft tissues. Elongated cheek teeth produce excessive pressure on tooth roots when the rabbit chews, causing deformation of the root, increased interproximal spaces and bending and rotation of the tooth itself. These processes contribute to increased cheek teeth malocclusion and worsening of dental disease. Ultimately bone is lost as roots perforate cortical bone. Fractures and tooth root abscesses are common sequela. In end-stage acquired dental disease of cheek teeth, eruption of teeth either is delayed or ceases altogether, and bone is reabsorbed. Causes of dental disease are summarized in table 1.