ODONTOGENESIS: STAGES AND THEIR CHARACTERISTICS - ANATOMY AND PHYSIOLOGY - 2025

The Odontogenesis or odontogenia is the process by which teeth develop. It begins with the appearance of the dental lamina, around the sixth or seventh week of gestation.

The basal layer of the epithelial lining of the oral cavity, derived from the ectoderm, proliferates from the sixth week of embryonic development and forms a horseshoe-shaped “band” called the dental lamina. This lamina develops in both the upper and lower jawbones.

First deciduous teeth of a Baby (Source: Chrisbwah via Wikimedia Commons)

Once this dental lamina is formed, the cells on the lower surface of the band experience an increase in their mitotic activity and invaginations originate that are introduced into the underlying mesenchyme. There are 10 shoots in each jaw.

These buds are the primordia of the ectodermal components of the teeth known as tooth buds, which initiate the budding stage of dental development. The subsequent development of each bud is similar, but asynchronous, and will correspond to the order in which each child's tooth sprouts.

From this point on, odontogenesis is divided into three stages: bud (bud), cap (cap) and bell (bell). During these stages, both the morphological and histological differentiation of the dental organ will take place.

In the human being, during its existence it will have two groups of teeth. At first 20 "milk" teeth, temporary or deciduous, which will later be replaced. In his adult stage, he will already have permanent teeth, specifically 32. Both the primary and permanent dentition are evenly distributed in both jaws.

Teeth have different morphological characteristics, a different number of roots and different functions.

Stages of odontogenesis and its characteristics

The developmental stages of odontogenesis are the budding or budding stage, the cap or crown stage, the bell and appositional stage, the formation of the root, and the formation of the periodontal ligament and related structures.

Budding stage

The budding or budding stage begins shortly after the development of the dental lamina, when the 10 buds or invaginations of the lower or deeper layer of the dental lamina reproduce in each jaw. 10 buds appear in the upper jaw and 10 mandibular buds.

The budding stage develops between the seventh and eighth week of intrauterine development and represents the first epithelial incursion into the ectomesenchyme. At this stage, the histological differentiation process has not yet begun.

The adjacent mesenchymal cells (originating from the neural crest) begin to condense around the ectodermal proliferations, forming what will later develop as the dental papilla.

Towards the posterior part of the maxilla and mandible, the dental lamina continues to proliferate and forms the successive or definitive lamina that will give rise to the dental buds of the permanent teeth, which do not have temporary predecessors and are the first, second and third molars. (12 molars in total or accessory teeth).

Crown stage

The crown or cap stage is characterized by an epithelial growth in the shape of a hat or cap, which is located on top of the ectomesenchymal condensation and which will form what is known as the enamel organ. At this stage, the enamel organ has three cell layers.

The ectomesenchymal condensation grows and forms a kind of balloon, which will give rise to the dentin and dental pulp. The part of the condensed ectomesenchyme, which delimits the papilla and encapsulates the enamel organ, will form the dental follicle or sac, which will then give rise to the supporting tissues of the tooth.

The enamel organ establishes the template of the presumptive tooth, that is, it takes the form of an incisor, molar or canine. This process is controlled by the enamel protrusion, undifferentiated cluster-shaped epithelial cells that make up one of the signaling centers for tooth morphogenesis.

The cells of the enamel bump synthesize and release a series of proteins at specific time intervals. Among these proteins are the bone morphogenic proteins BMP-2, BMP-4, and BMP-7 and fibroblast growth factor 4 (FGF-4).

These inducer proteins have the function of forming the cusps of the teeth and, for this, the pons cells require the presence of epidermal growth factor (EGF) and FGF-4. Once the pattern of the cusp of the teeth is formed, the EGF and FGF-4 disappear and the cells of the enamel bump die.

X-ray showing a deciduous tooth and the crown of a permanent tooth (35,36,37) (Source: Nizil Shah via Wikimedia Commons)

The set formed by the dental papilla and the enamel organ is called the germ of the tooth. At this stage of development, a thick, solid cord of epithelial cells appears deep with respect to the ectomesenchyme, called the surrogate lamina.

In this lamina, some buds or buds will develop that are the precursors of the substitute teeth, which will then replace the deciduous ones that are developing.

Bell and appositional stage

This stage develops around the third month of intrauterine life. Histologically it is recognized because the enamel organ acquires its final conformation with four cell layers: the outer enamel epithelium, the stellar reticulum, the intermediate layer and the inner enamel epithelium.

The appearance of the intermediate layer of the enamel organ is what characterizes this stage. It is the stage of morpho-differentiation and histo-differentiation. Simple squamous cells in the inner enamel epithelium develop into enamel-producing columnar cells called ameloblasts.

The more peripheral cells of the dental papilla then differentiate and form the cylindrical dentin-producing cells called odontoblasts. As a result of the differentiation of ameloblasts and odontoblasts, dentin and enamel begin to form.

Dentin and enamel abut each other and this junction is called the dentin-enamel junction (DEJ). The tooth is then said to be in the appositional stage of odontogenesis. In the process of dentin formation, the odontoblasts emit extensions that are lengthening from the UDE.

These extensions form the cytoplasmic extensions called odontoblastic processes, which are surrounded by dentin and then leave the space to form the dentinal tubule.

The ameloblasts also move away from the DEUs and form what is called the Tomes process. The ameloblasts are secreting the enamel matrix which is contracting its apical portion, forming the Tomes process.

This contraction zone is then expanded by the formation of more enamel matrix, and the process is repeated successively until the enamel matrix is ​​no longer produced. As calcification of the dentin matrix occurs and the definitive dentin is formed, the calcification process extends to the enamel matrix and the enamel is shaped.

Root formation

Once the enamel and dentin of the crown have been formed, the odontogenic process, starting from the germ of the tooth, passes to the stage of root formation. The internal and external epithelia of the enamel organ elongate and form a kind of "sleeve" that is called the epithelial sheath of the root of Hertwig (VERH).

The outermost cells of the dental root papilla undergo differentiation and become odontoblasts that initiate the formation of the root dentin matrix. As this occurs, the VERH lengthens and begins to disintegrate near the apical portion.

This process leaves perforations through which some ectomesenchymal cells of the dental sac migrate and differentiate into cementoblasts. These cells begin to synthesize and release cementum matrix, which then calcifies and forms dental cementum.

As the root lengthens, it approaches the crown and, finally, it sprouts into the oral cavity.

Periodontal ligament, alveoli and gingiva

The periodontal ligament is a collagenous connective tissue that fixes and suspends the tooth in the socket. This ligament is located in a space between the root cementum and the bone socket. It is a richly innervated area.

The alveolus is the depression or bony hole within the maxillary and mandibular bone that houses each tooth root. The gingiva is attached to the enamel surface by a squamous wedge-shaped epithelium called the junctional epithelium.

References

1. Gartner, LP, & Hiatt, JL (2010). Concise Histology E-Book. Elsevier Health Sciences.
2. Golonzhka, O., Metzger, D., Bornert, JM, Bay, BK, Gross, MK, Kioussi, C., & Leid, M. (2009). Ctip2 / Bcl11b controls ameloblast formation during mammalian odontogenesis. Proceedings of the National Academy of Sciences, 106 (11), 4278-4283.
3. Gonzalo Feijoó García (2011) Chronology of the odontogenesis of permanent teeth in children of the community of Madrid: application to the estimation of dental age. Complutense University of Madrid Faculty of Dentistry Department of Prophylaxis, Pediatric Dentistry and Orthodontics. ISBN: 978-84-694-1423-1
4. Langman, J. (1977). Medical embryology. Williams and Wilkins, Baltimore, MD.
5. Slavkin, HC, & Bringas Jr, P. (1976). Epithelial-mesenchyme interactions during odontogenesis: IV. Morphological evidence for direct heterotypic cell-cell contacts. Developmental biology, 50 (2), 428-442.