1. Initiation Stage:
At the beginning of the sixth week, the embryo’s primitive mouth is lined by ectoderm. The outer position of the ectoderm gives rise to oral epithelium which consists of horse shoe shaped band of tissue. There is a base membrane, which separates developing oral epithelium and mesenchyme.
During the later portion of the seventh week, the oral epithelium grows and produces a layer known as dental lamina. The dental lamina starts to form in the mid line for both arches and periodically develops.
2. Bud Stage:
This stage is mainly characterised by the appearance of a tooth bud without the clear arrangement of cells. The tooth bud itself is the group of the cells at the end of the dental lamina. The stage is named for the extensive proliferation into bds. Each of these buds from the dental lamina, together with the mesenchyme will develop into a tooth germ. The important point to note is that only the proliferation of the two tissues occurs during this stage.
3. Cap Stage:
4. Bell Stage:
- Inner enamel epithelium
- Outer enamel epithelium
- Stellate reticulum
- Stratum intermedium
At the same time, the dental papilla undergoes differentiation and produces two types of cells:
- Outer cells of the dental papilla that forms the dentin secreting cells (odontoblasts).
- Central cells of the dental papilla which forms the primordium of the pulp
The dental sac (follicle) increases its collagen content and differentiates at a later stage than the enamel/dental organ and the dental papilla.
5. Apposition Stage:
6. Maturation Stage (Crown Stage):
Odontoblasts (The dentin forming cells):
These are different from the mesenchyme of the dental papilla and it occurs after the differentiation of pre-AB begins. They begin secreting an organic matrix, closest to the area of the future cusp of a tooth, and this organic matrix contains collagen fibres. The odontoblasts are responsible for the odntoblasts process.
The odontoblasts process causes the secretion of hydroxyapatite crystals and the mineralisation of the matrix. This area is known as mantle dentin. Mantle dentin forms from the pre-existing ground substance of the dental papilla. Primary dentin forms through different process whereas the secondary dentin is formed after finishing of the root formation. Tertiary dentin (reparative dentin) forms as a result of stimuli for example dentin carries.
Enamel formation is known as Amelogenesis and occurs in the crown stage of the tooth development. Generally speaking, the enamel formation takes place in two stages: the secretion and maturation stages.
In the secretion stage, ameloblasts release enamel proteins that contribute to the enamel matrix. The appearance of this mineralised tissue occurs usually around the third or fourth month of pregnancy.
In the maturation stage, the ameloblasts transports some of the substances used in formation of enamel out of the enamel and so the function of ameloblasts also changes into the transportation of substances. Most of the minerals transported by ameloblasts in this stage are proteins used to complete mineralisation. By the end of this stage, the enamel has completed its mineralisation.