Pulp cavity

Teeth have a transparent outer layer of enamel which is about 2 mm thick, and an inner layer of white dentine which surrounds the innermost pulp cavity where the nerves are located. Both the enamel and the dentine are calcium phosphate, a mineral that can exist in various forms, that of the enamel layer being hydroxyapatite, which is one of the hardest naturally occurring minerals. When this is exposed to fluoride it forms an even harder mineral fluoroapatite. Unfortunately both this and hydroxyapatite are slightly porous and this is why teeth become stained by chemicals such as polyphenols and other dark coloured substances that are present in coffee, tea, red wine, bilberries, blueberries, and cigarette smoke. (Staining can also be caused by tetracycline antibiotics, especially when taken by children whose teeth are developing. This type of discoloration is permanent, which is why such antibiotics are now only prescribed for adults.)... 

A tooth consists of three basic parts, the crown, which is exposed, the neck, which is at the gum line, and the root, which is embedded in the gum andjaw. The crown may be completely or partially covered with a harder substance known as enamel. The bulk of the tooth is composed of dentine, which surrounds and protects the inner pulp cavity. Pulp is vascular tissue that contains nerves and blood vessels, fed from below through a narrow channel in the dentine called the root canal. The root of the tooth is also surrounded by... 

Dentine is composed of a mixture of about 70% hydroxlyapatite (Ca5(P04)3(0H)), 20% collagenous proteins and about 10% water. The microscopic structure of dentine consists of microscopic canals called dentinal tubules that radiate out from the pulp cavity to the cementum border. The diameter of these canals varies among different animals, and ranges... 

Tusk is a general term used to describe large teeth that protrude beyond an animal s lips, such as those produced by elephants and walrus (Figure 6.16). Tusks tend to grow throughout an animal s lifetime, and contain a live, open-pulp cavity. Tusks have two basic layers an outer homogeneous and finegrained dentin, and an inner, coarser dentin mass that is created from within, in the pulp cavity. 

Dentin comprises the bulk of the vertebrate tooth (Fig. 1.5). During the formation of the tooth, dentin is produced by cells located in the pulp cavity [25, 26]. 

Figure 1.5. Transverse section through a mouse incisor tooth. E, enamel D, dentin P, pulp cavity. Note the dentin tubules, radiating out from the pulp cavity to the...

The cells continuously withdraw as they form more dentin, and the pulp cavity decreases in size. The zone of formation between the cell surface and the final mineralized product is usually only a few tens of micrometers thick (Fig. 1.6). It is known as the predentin. Many rodents have continuously forming incisors. They, like the chiton teeth, are ground away at one end, and are continuously replaced. Thus all stages of tooth formation can be studied in a single rodent incisor. In the rat tooth the stages merge into each other, and are not separated, as is the case in the chiton tooth. 

Di nosdc for walrus ivory is that it is the only ivory to contain primary and secondary dentine. The former displays very finely packed, concentric lines and makes up the bulk of the tusk. The latter has a bubbly appearance like that of tapioca or rice pudding (Figs 3.3 and 3.16). It fills the centre of the tusk all the way through from the tip to a small pulp cavity in the part of the tusk attached to the jawbone. This secondary dentine looks more fragile than the primary dentine, but it has the same hardness, and the material can be carved and polished with Htde regard to the difGerent textures (Fig. 3.3). 

Mature enamel is a cell-free tissue while cementum though minerahzed is avascular, similar to some bone tissues, and may have developed to serve the local needs, not a primitive, but a derived and modulated tissue system (Poole, 1967). The bulk of the mineralized tooth is dentine, also a vital tissue that contains passageways known as tubules that are intermineralized with apatite. The tubules reach from the pulp cavity with its supply of nerves and blood vessels that enter at the base of the root(s) and extend to the enamel. Dentine has the possibility to repair itself. 

The composition of dentin is similar to that of bone, with crystal sizes of about 50 x 25 x 2 nm3, much smaller than those in enamel. Dentine connective tissue comprises a network formed by randomly intertwined mineralised collagen fibrils permeated by tubules that radiate from the pulp cavity towards the dentin-enamel junction (Figure 3.4c). 

The smear layer is formed during the cavity cutting process and can consist of cutting debris, smeared odontoblasts (one of a layer of connective tissue cells lining the pulp cavity, which takes place in the formation of dentine) and micro-organisms. It cannot be formed in a reproducible manner. There are three main approaches to dealing with the smear layer. 

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