Page 775 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

750 CHAPTER 4

VetBooks.ir 4.62 4.63

Fig. 4.63 Overgrowths on the buccal and
lingual aspect of the cheek teeth. (Photo courtesy
Graham Munroe)

Fig. 4.62 Increased wear of the incisors of a horse
that crib bites. (Photo courtesy Graham Munroe)

ABNORMALITIES OF WEAR wear on the palatal aspect of the maxillary arcade
OF THE CHEEK TEETH and of the buccal aspect of the mandibular arcade.
Factors that limit lateral jaw movement can result
FOCAL DENTAL OVERGROWTHS, in exaggeration of the angle of the occlusal sur-
DENTAL POINTS, SHEAR MOUTH face, causing dysmastication and uneven wear over
the tooth. Ultimately, this leads to the develop-
Definition/overview ment of focal overgrowths (due to reduced attrition)
During normal mastication in the horse the man- especially on the lingual aspects of the mandibular
dible is lowered and then raised in a dorsal move- teeth and the buccal aspects of the maxillary teeth
ment, circumducting from buccal to lingual. This (Fig. 4.63).
brings the mandibular teeth into occlusion in an
axial direction so that the occlusal surfaces shear Clinical presentation
over each other in a grinding action. This is referred These focal overgrowths develop sharp enamel
to as the ‘power stroke’ and is driven by the power- points, which can impinge on soft tissue causing
ful masseter and pterygoid muscle groups. Due to masticatory pain and ulceration. Overgrowths of the
the anisognathism in the equine mouth, only one lateral processes of the buccal aspect of the maxillary
molar arcade is in occlusion during each masticatory teeth can become particularly prominent.
stroke. The temporomandibular joint is maintained
by a tight joint capsule and permits free lateral move- Diagnosis
ment and a degree of rostrocaudal movement. When Such overgrowths are detected by extraoral and intra-
the horse lowers its head into a grazing position, oral digital palpation during thorough routine exami-
the mandible drops and moves rostrally and normal nations, and are particularly prevalent on the 10s and
occlusion would be expected at this point. 11s. Examination using a mirror or oroscope reveals
mucosal trauma and the extent of the overgrowth.
Aetiology/pathophysiology Continuing development of these overgrowths can
The range of lateral movement of the mandible result in occlusal angles approaching 45º, termed
appears to be wider when chewing grass or forage ‘shear mouth’ (Fig. 4.64). These grossly exaggerated
than concentrate processed feeds. The rotary chew- overgrowths physically prevent lateral masticatory
ing action is reflected in the angled occlusal surface movement, resulting in a scissor-like action, and fur-
(10–30º to the horizontal), and results in increased ther exacerbation of the problem ensues.