Biomedical Engineering Reference
collagen, with minor contributions from phosphoproteins, glycoproteins,
proteoglycans, and some plasma proteins [ 30 ]. The composition of dentinal fluid
is reportedly similar to plasma [ 29 ].
Features of the dentin structure include the tubules that traverse the structure
from the pulp cavity to the region just below the dentin-enamel junction (DEJ) or
the dentin-cementum junction. The tubules, which could be modeled as narrow
tunnels a few microns or less in diameter, represent the tracks taken by the
odontoblastic cells from the pulp chamber to the respective junctions. Dentinal
tubule diameter measures approximately 2.5 m m near the pulp and 0.9 m m near the
DEJ [ 31 ]. Tubule density and orientation vary from location to location; density is
lowest at the DEJ and highest at the predentin surface at the junction to the pulp
The number of tubules in young premolar and molar teeth ranges from 50,000 to
75,000 per square millimeter at the pulpal surface to approximately half as many
per square millimeter in the proximity of the DEJ [ 27 ]. The content of the tubules
include fluid and odontoblast processes for all or part of their course. In contrast to
root dentin, the tubules in coronal dentin are surrounded by a collar of highly
mineralized peritubular dentin [ 32 ].
The composition of the peritubular dentin is carbonate apatite with very small
amounts of organic matrix, whereas intertubular dentin, i.e., the dentin separating
the tubules, is type I collagen matrix reinforced with apatite. Thus, the composition
of intertubular dentin is primarily mineralized collagen fibrils; the fibrils are
described as a composite of a collagen framework and thin plate-shaped carbonated
apatite crystals whose c-axes are aligned with the collagen fibril axis [ 33 ]. In
healthy dentin, the majority of the mineralized collagen fibrils are perpendicular
to the tubules [ 34 ]. It is important to recognize that the composition of dentin is not
static. It is influenced by the relative position of the dentin within the tooth, the age
of the dentin, and the presence and/or absence of disease [ 29 ].
7.2.1 Altered Forms of Dentin
In contrast to enamel, dentin is a vital tissue containing the cell processes of
odontoblasts and neurons. Since the odontoblasts can be stimulated to deposit more
dentin, this tissue is capable of limited repair. The structure-property relationships of
dentin vary with location, physiological, aging, and disease processes.
The composition, mineralization, and structure are different between normal and
altered forms of dentin [ 27 , 29 , 31 , 33 ]. A wide variety of terms have been used to
describe the types of dentin associated with physiological aging and disease
processes. Descriptors such as secondary, tertiary, sclerotic, and transparent dentin
have all been used. In general, secondary dentin forms as a result of normal
physiologic stimuli, whereas tertiary or reparative dentin forms as a result of a
pathologic process such as caries. The rate of secondary dentin deposition is
generally slower than the rate associated with primary or initial dentin deposition.