Biomedical Engineering Reference
In-Depth Information
Table 8-1. Conditions under which teeth operate. 2
Rate of chewing
60-80 cycles/min
Forces: maximum biting force overall teeth
maximum biting force on a single tooth
normal forces on a single tooth
640 N
265 N
3-18 N
Contact time: time maximum pressure sustained
0.07 S
Total contact time: normal
Bruxist (over 24 h)
10 min
30 min - 3 h
Mean sliding distance
1.0 mm
15 mm 2
Contact area (1st molar region)
Maximum stress
20 MPa
tissue is not repairable. Some typical physiological conditions of teeth
have been listed in Table 8-1 by Waters. 2 Recently, investigations
indicate that masticatory loading forces teeth are exposed to range from
28 N to more than 1200 N. 3,4 At the same time, the contact area may be
as small as a few square millimeters. It is amazing that enamel can
sustain and survive such high forces for millions of cycles. The
mechanical properties and the deformation mechanisms in relation to the
compositional and hierarchal microstructural characteristics of enamel
are an essential factor to understand this natural material.
As the inner layer of tooth hard tissue, dentin is much softer than
enamel. This may be appreciated from the following aspects: structurally,
as odontoblasts penetrate into dentin tubules, dentin and pulp are usually
considered as a vital complex in response to bacterial invasion;
compositionally, dentin has much higher organic component than enamel;
functionally, because its major role is to protect the pulp rather than
mastication, the mechanical property requirements of dentin are for
toughness rather than hardness as for enamel.
Hierarchical microstructures and precisely distributed organic
components endow dental hard tissues excellent anisotropic mechanical
properties, which ensure their life-time survival in the mouth as a load
bearing organ. To understand and illustrate the basis for the excellent
performance of tooth tissues, many investigators have undertaken
various mechanical tests on them. Moreover, knowledge of the
mechanical properties and microstructural features of enamel and dentin
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