Definitions and Descriptions

Human mouth develops three distinct teeth sets: deciduous (milk teeth), mixed (during teeth change) and permanent (adult)

The deciduous dentition is made up of 20 teeth that, normally, begin to appear in the child's mouth around his sixth month of age and are full set approximately at his second year.

A deciduos teeth set is composed by:

  • 2 sup. + 2 inf. central incisives
  • 2 sup. + 2 inf. lateral incisives
  • 2 sup. + 2 inf. canines
  • 4 sup. + 4 inf. milk molars

Starting at the age of 6, a long period begins in which the child performs a full change of the milk teeth set and aquires some additional new teeth. At the end of the process, approximately around the age of 12, the permanent teeth set will be composed of 28 teeth. Further than that, 4 more teeth (the wisdom teeth) are aquired (but not always) within the 18th year of age, but their presence is all but granted. If these appear, the total number of permanent teeth rises up to 32.

A permanent teeth set is composed by:

  • 2 sup. + 2 inf. central incisives (in replacement for the homologous milk teeth)
  • 2 sup. + 2 inf. lateral incisives (in replacement for the homologous milk teeth)
  • 2 sup. + 2 inf. canines (in replacement for the homologous milk teeth)
  • 4 sup. + 4 inf. premolars ((in replacement for the milk molar teeth)
  • 6 sup. + 6 inf. molars (additional and considering the wisdom teeth)

The human tooth is divided in two anatomical parts, only one of which is visible. The Crown, which is the part that emerges from the gum and which we are able to see when having a look into our mouth, and the Root, which is the invisible part, sinked below the gum and anchored to the bone.

Teeth differ in form and dimensions, but all of them are formed by 4 structures: we'll describe them one by one starting from the innermost towards the surface.

a) Pulp

Familiarly called "nerve", it's the innermost part of the tooth. It's a living tissue containing blood vessels, nerves and various kinds of cells. It's the only portion of the tooth to have a real metabolism, and is the part that "hurts" if reached by a caries.

b) Dentine

It's the rigid case enveloping the pulp for all its length, from the crown to the root of the tooth. It's a mainly calcified structure which also contains some organic components such as cells that consent it to partially modify its anatomy and, in particular, the dentin is able to create calcium deposits that protect the pulp for external injuries.

c) Enamel

The hardest part of the tooth (and of all our body) is really a crystalized shell, a calcified cap that has the function of supporting the chewing forces. It covers the tooth only down to its neck, so it's actually the visible crown of the tooth itself, stopping at gum's height.

d) Root Cementum

It's the analogous of the enamel on the non visible part of the tooth, the root that is. It's a thin layer covering the root itself but differently from the enamel, it's much less hard. It's the portion of tooth that emerges when the gum and bone level skips lower, causing a lenghtening of the neck. It's function is to connect the tooth to the bone.

At the moment of birth, man has a sterile mouth. This status is nonetheless of very short duration because the newborn swiftly aquires a bacterial flora through contacts with his surroundings, food, contact with the mother, objects carried to his mouth and so on.

All this leads to the fact that a stantial bacterial flora composed by various species, some of them dangerous for oral health, settles in the mouth.

Bacteria in the oral cavity live clutched together on dental surfaces, on the mucosa, on the tongue. They pile up in great quantity building a smeary structure together with proteic filaments.

This structure is known as the Bacterial Plaque. It mostly is to be found around the teeth's collar, where they emerge from the gum and in the areas between teeth (interdental space). Some plaque bacteria live by capturing sugar and carbohydrates being found in the mouth during the food chewing act and produce lactic acid and other substances as a dejection result.

Lactic acid is able to corrode enamel causing its dissolution: this is the pathological mechanism by which the caries works.

The substances produced by plaque, also have an action on the gum, causing gengivitis and in a more advanced stadium, periodontitis.

Bacterial plaque easily tends to harden and forms hard layers on the teeth, that are called Dental Calculus.