Page 748 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Gastrointestinal system: 4.1 The upper gastrointestinal tr act 723

VetBooks.ir produce the dentine bridge that maintains the sepa- 4.2 5 5
ration between the pulp and oral cavity. The 1 and
st
6 cheek teeth typically have an additional pulp
th
horn at the rostral and caudal aspect, respectively 3 3 4 4
(Fig. 4.2). Research using computed tomography 6
(CT) has revealed a complex arrangement of anasto- 1 1 2 2
moses and connections between the pulp horns, the
common pulp chamber and the roots of the tooth.
The apices of the first two cheek teeth and the ros-
tral root of the third typically lie in the maxillary
bone. The remaining roots of the third tooth and
those of the fourth cheek tooth lie in an alveolus in Fig. 4.2 Occlusal view of right maxillary dentition,
close association with the rostral maxillary sinus. teeth 106 and 107 showing occlusal secondary dentine
The alveoli surrounding the apices of the fifth and (white arrow) overlying pulp horns (labelled 1–6) and
sixth cheek teeth lie in the caudal maxillary sinus infundibular enamel (red arrow).
on each side. The position of the maxillary septum
dividing rostral and caudal maxillary sinus and the resistance to cracking. Dentine comprises of columns
roots of the triadan 09 (1 molar, 4 cheek tooth) of primary, tubular dentine, with intertubular dentine
th
st
can commonly lie in the caudal compartment. inbetween them, and is actively metabolic with viable
The mandibular cheek teeth have no infundibula, odontoblast processes laying down the dentine con-
but have infolding of the peripheral enamel, which centrically before receding. Dentine can be catego-
creates ridges on the occlusal surface once they are rised into primary and secondary dentine. Secondary
in wear. Each of the first five teeth in the mandibular dentine is produced by the odontoblasts lining the
arcade have five or six pulp horns that anastomose pulp in response to attrition at the occlusal surface
into two major roots, with the sixth having an addi- and maintains the physical barrier between the oral
tional pulp cavity and a smaller root. The maxillary cavity and the pulp (Fig. 4.3). Equine pulp is rich
arcade is 23–30% wider than the mandibular arcade in stem cells, consists of a meshwork of connective
at any point (anisognathism). The apices of the man- tissue, reticulin fibres, with vascular and neurologi-
dibular cheek teeth lie in the mandible and they are cal elements. In hypsodont teeth, continuous second-
aligned in an approximately straight line. ary dentine production balances occlusal attrition
throughout the life of the tooth. The vasculature
Composition of equine teeth in the pulp passes through wide apical foramina in
Equine teeth are composed of a laminate of three young horses to fulfil the metabolic requirements
mineralised tissues arranged around the dental pulp, of the active odontoblasts. The apical foraminae are
which contains the nervous and vascular supply to the narrowed in aged horses.
tooth. Equine dental enamel is the hardest substance Cement is similar to bone in composition com-
in the skeleton, comprising 96% inorganic hydroxy- prising approximately 65% impure hydroxyappatite
apatite crystals produced by the ameloblasts of the crystals. It lines the reserve crowns of the teeth and,
germinal epithelium. Once this is disrupted enamel in the case of the incisors and maxillary cheek teeth,
production ceases (after the tooth is approximately 2 lines the infundibula and provides an attachment of
or 3 years old). There is no self-reparative process in the periodontium to the alveolar bone. The periph-
enamel. It does have very high wear resistance, which eral cementum grows throughout life, whereas the
makes it vulnerable to cracking along lines of weak- infundibular cement is devoid of vascularity, is vari-
ness. Dentine is the second hardest skeletal tissue and ably incomplete and can be considered as inert tissue.
comprises 70% of the mass of the tooth (a percent- The periodontal ligament complex consists of a layer
age that increases with age). It is composed of 70% of vascular innervated connective tissue comprising
hydroxyapatite and 30% organic tissues, which gives the cementum, collagen and the alveolar periosteum.
it a higher elasticity than enamel and an increased The collagen fibres, termed ‘Sharpie’s’ fibres, suspend