Introduction to Teeth - Dental Biotribology - page 6

Lingual

Central
(or Incisors)

Lateral

1st Molar

Posterior

Anterior

2nd Molar

1st Bicuspid

Buccal

Cuspuid/
Canine

2nd Bicuspid

Fig. 1.2 Human tooth orientation [ 26 ]

which has a different function. Incisor teeth are used for shearing, the canines
evolved for holding prey, and molars are used for chewing. In general, molars have
complex surfaces and cusps that fit together in a dynamic way during the chewing
process. Figure 1.2 also illustrates different surfaces of teeth. The buccal side is
nearest the side to the lips or cheek; the lingual side is closest to the tongue. The
occlusal surface, the main site of tooth wear processes, is the side that meets a tooth
or restoration material in the opposite jaw during chewing or biting. In addition, the
side of one tooth in contact with a proximal other tooth is defined as the approximal
surface; each tooth has two approximal surfaces.

1.4 Biomechanics of Human Teeth

Mastication is the most important function of teeth. It has been widely accepted that
wear of dental materials in the mouth mainly results from chewing cycles. Therefore,
it is important to understand the biomechanics of mastication. Mastication is the
action of chewing food, which is a complex and compound process [ 27 ]. Mastication
involves two stages: the open phase and the closed phase [ 28 ]. During the first stage,
the teeth are brought by the jaw from the open position to a position of contacting
the food bolus. Normally, no occlusal forces are involved in this phase (sticky foods
represent an exception), and the abrasive particles are suspended and free to move
in the food slurry. The second stage starts when the teeth first contact the food bolus
and continues until the jaw begins to open. During this phase, occlusal loads are
applied and distributed through the food bolus so the food particles are trapped
between the opposing surfaces of teeth (especially the upper and lower molars) and
dragged across them. Therefore, the food bolus is compressed and crushed, and then
grinding occurs with either tooth-food-tooth (or indirect) or direct tooth-tooth