Anatomy and Disorders of the Oral Cavity of Rat-like and Squirrel-like Rodents

Abstract

The order Rodentia comprises more than 2000 species divided into 3 groups based on anatomic and functional differences of the masseter muscle. Myomorph and sciuromorph species have elodont incisors and anelodont cheek teeth, unlike hystrichomorph species which have full anelodont dentition. Diseases of incisors and cheek teeth of rat-like and squirrel-like rodents result in a wide variety of symptoms and clinical signs. Appropriate diagnostic testing and imaging techniques are required to obtain a definitive diagnosis, formulate a prognosis, and develop a treatment plan. A thorough review of elodontoma, odontoma, and pseudo-odontoma is provided, including treatment of pseudo-odontomas in prairie dogs.

Apical Elongation of Molar Teeth in Captive Microtus Voles

“…Pseudo-odontoma was considered appropriate for some of the dysplastic changes, particularly the abnormal matrigenesis, observed at the molar apices but not for the masses of markedly disrupted, haphazardly organized and proliferative odontogenic epithelium. Despite these challenges, the gross and histopathologic features here are very similar to those described in rat-like and squirrel-like rodents, 1,2,13,22 rabbits, 17 and other voles 29 though less proliferative and destructive than those described in guinea pigs and degus. 2,4,16,19,23 Observations in CSF-1-deficient, 14 Snx10-deficient and bisphosphonate-treated (personal observations, D. Imai) osteopetrotic rodents have confirmed that microtraumatic disruption and fragmentation of odontogenic epithelium by bone can produce isolated and disorganized islands of proliferative odontogenic epithelium that can subsequently proliferate into odontoma-like masses.…”

“…In the absence of direct occlusal contact and vertical pressure, coronal eruption may not be inhibited as quickly and apical elongation may be delayed. This difference in occlusal apposition and masticatory force between molar and incisor teeth and the absence of any repetitive incisor trauma 1,2,22 could explain why apical elongation (with one exception in the California vole collection) was not observed in the incisors of the Amargosa voles. Histopathologic incisor apical abnormalities may still be present in the Amargosa voles, but were not evaluated in this study.…”

An Investigation of the Wild Rat Crown Incisor as an Indicator of Lead (Pb) Exposure Using Inductively Couple Plasma Mass Spectrometry (ICP-MS) and Laser Ablation ICP-MS

“…The inherent incisor tooth structural variations between the root and crown due to the larger part of the dental root pulp and higher dentine crown mass, as well as dentine-enamel ratio, could be the key factors in the accumulation of Pb-T differences [ 33 ]. The rodent incisors are predominantly dentine with a thin layer of enamel located only in the front part of the tooth [ 30 ]. The influence of the presence of the large dentine mass in the crown of incisor teeth may have been one of the contributing factors behind the L2 or U2 in the low Pb group accumulating much Pb than the L1 or U1 in the high Pb exposure group.…”

“…However, the present findings agreed in part with a report in human incisor teeth samples where most of the Pb were primarily deposited in the secondary dentine region close to the pulp, and secondarily, at surface enamel [ 12 ]. Moreover, the observed high intensities of Pb in the outer part of incisors were only on the front side, the only side bearing enamel in rodent incisors [ 30 ]. This phenomenon has been demonstrated in both erupted and non-erupted teeth that highly accumulated Pb in the outer enamel surface and with a gradual reduction of Pb in the deeper layers of the enamel [ 19 , 39 , 44 , 45 ].…”

“…Briefly, the teeth samples were placed in an ultrasonic bath of L-cysteine (Cica reagent, 100 mg/L; Kanto Chemical, Tokyo, Japan) for 5 min followed by rinsing in an ultrasonic bath of distilled water for 10 min prior to drying. The samples were then dried in an oven at 54 °C for 48 h. Each tooth was divided into two subdivisions using the yellow-orange pigmentation of enamel on the crown part of the labial surface of the tooth [ 30 ] as a distinguishing reference mark as illustrated in Figure 2 . Each lower (L) incisor was divided into two subdivisions, namely, L1 (root) and L2 (crown).…”