Page 544 - Textbook of Pathology, 6th Edition

528 Cementum is the portion of tooth which covers the dentin at
the root of tooth and is the site where periodontal ligament
is attached. Cementum is similar to bone in morphology and
composition.
Dental pulp is inner to dentine and occupies the pulp cavity
and root canal. It consists of connective tissue, blood vessels
and nerves.
Nests of odontogenic epithelium are normally present in
the jaw and may develop into cysts and tumours.
DENTAL CARIES
Dental caries is the most common disease of dental tissues,
causing destruction of the calcified tissues of the teeth.
ETIOPATHOGENESIS. Dental caries is essentially a
disease of modern society, associated with diet containing
high proportion of refined carbohydrates. It has been known
for almost 100 years that mixture of sugar or bread with
saliva in the presence of acidogenic bacteria of the mouth,
especially streptococci, produces organic acids which can
decalcify enamel and dentin. Enamel is largely composed
of inorganic material which virtually disintegrates. Dentin
contains organic material also which is left after
decalcification. Bacteria present in the oral cavity cause
proteolysis of the remaining organic material of dentin,
completing the process of destruction. Diets rich in
Figure 19.7 The normal structure of tooth in longitudinal section carbohydrates do not require much chewing and thus the
embedded in the jaw.
soft and sticky food gets clung to the teeth rather than being
cleared away, particularly in the areas of occlusal pits and
the portion of oral mucosa called the gingiva or gum, and fissures. ‘Bacterial plaques’ are formed in such stagnation
SECTION III
that they are part of a highly specialised odontogenic areas. If these plaques are not removed by brushing or by
apparatus; other parts of this apparatus being the mandible vigorous chewing of fibrous foods, the process of tooth
and maxilla. decay begins. There is evidence that consumption of water
Embryologically, odontogenic development takes place containing one part per million (ppm) fluoride is sufficient
from primitive structure, the dental lamina or primitive oral to reduce the rate of tooth decay in children.
cavity, as follows: MORPHOLOGIC FEATURES. Caries occurs chiefly in the
Inner epithelial layer of the dental lamina is ectoderm-
derived columnar to cuboidal oral epithelium called areas of pits and fissures, mainly of the molars and
premolars, where food retention occurs, and in the cervical
ameloblasts which secrete enamel matrix, also called enamel part of the tooth.
organ. Grossly, the earliest change is the appearance of a small,
Mesoderm-derived connective tissue gives rise to
Systemic Pathology
structures in the dental papilla (i.e. dental pulp or core of chalky-white spot on the enamel which subsequently
enlarges and often becomes yellow or brown and breaks
loose connective tissue, blood vessels and nerves). down to form carious cavity. Eventually, the cavity
Outer margin of the dental papilla differentiates into becomes larger due to fractures of enamel. Once the lesion
odontoblasts, which continue with ameloblastsic epithelium;
odontoblasts secrete dentin.
The normal structure of tooth in an adult is as follows
(Fig. 19.7):
Enamel is the outer covering of teeth composed almost
entirely of inorganic material (as in bone) which can be
demonstrated in ground sections only as it is lost in
decalcified section.
Dentin lies under the enamel and comprises most of the tooth
substance. It is composed of organic material in the form of
collagen fibrils as well as inorganic material in the form of
calcium phosphates as in bone. Dentin is composed of
odontoblasts or dentin cells which are counterparts of
osteocytes in bone but differ from the latter in having
odontoblast processes. Dentin in the crown of tooth is covered Figure 19.8 Dental caries. There is complete destruction of enamel,
with thicker layer of enamel. deposition of secondary dentine and evidence of pulpitis.