MORPHOGENESIS OF DENTAL ARCHES
The plan:
Introduction
1 Reminders:
1- embryological development of the dental arch.
2. Tooth eruption
2.1 Definitions
2.2 Phases of dental eruption
2.2.1 Passive Eruption Phase
2.2.2 Active Pre-Functional Eruption Phase
2.2.3 Functional Implementation
2.2.4 Occlusal Adaptation
2.3 Biological mechanisms of dental eruption
2.4 Chronology of normal eruption
2.4.1 Eruption of temporary teeth.
2.4.3 Eruption of permanent teeth.
3. The stages of dental arch morphogenesis
3.1 Phase of formation of temporary teeth
3.2 Stable temporary dentition phase
Conclusion
introduction
The normal morphogenesis of dental arches has long been considered a fully known phenomenon that should naturally lead to well-aligned arches in “normal” occlusion according to ANGLE’s concept. During the 1950s, the descriptive and analytical study of the morphogenesis of the arches experienced a renewed interest. It then appeared that the relationships of the teeth between them, and of the arches with their antagonists, vary during childhood and adolescence.
Definition
The term morphogenesis comes from the Greek morphe which means “form” and genesis, “to be born”. Morphogenesis is therefore the set of processes that determine the structure of a body. In a living being, the structure takes shape during the development of tissues and organs. Its realization is determined by genetic expression and by a set of physicochemical phenomena. The morphogenesis that takes place during development will lead to an adapted form.
1-Reminders:
1-1- Embryological development of the dental arch:
It is from the 4th week of intrauterine life after the completion of the neurulation phase that the human embryo will be transformed by an antero-posterior movement, from a tubular embryo with a rather straight appearance to an elongated shape with dorsal convexity and two new territories: the cranial pole (cephalic) and the caudal pole (constituting the cardiac outline). The space delimited by these two structures is called stomodeum; precursor of the oral cavity. This same antero-posterior movement is the origin of the formation of folds leading to the pharyngeal arches. (Fig 1)
Fig. 1: Cephalic inflection and formation of the stomodeum
- Formation of facial buds
Around the 28th day of development, there will be lateral cell proliferation at the level of the anterior part of the 1st branchial arch. This cell mass splits, resulting in the formation of the maxillary bud in its upper part and the mandibular bud in its lower part. While around the 35th day of development, the nasal bud will appear at the level of the anterior part of the frontal bud.
- Formation of the odontogenic epithelium:
On the upper part of the mandibular bud and the lower part of the maxillary bud and the nasal bud, we notice the development of an epithelium different from the oral epithelium: this is the odontogenic epithelium, and this, around the 30th day for the first two buds and the 36th day for the last. (Fig.2)
fig2 Distribution of odontogenic epithelium on the 36th day
The different epithelia from the four upper buds will fuse around the 38th day to form a single continuous odontogenic epithelium (OE). The same phenomenon also occurs for the epithelia of the mandibular buds
- Fig 3: Distribution of the odontogenic epithelium on the 38th day
This odontogenic epithelium which will be at the origin of the future dental arch. It will initiate the beginning of the formation of a particular organ: the dental organ.
The genesis of this dental organ depends on an exchange phenomenon between the epithelium and the underlying mesenchyme. This phenomenon is possible thanks to the intervention of various molecules ensuring the exchange signals
Little by little, this epithelial thickening will split and lead to the formation of two continuous epithelial laminae: the vestibular lamina and the dental lamina.
- The primitive dental blade or plunging wall:
At the 6th week of development, a proliferation of epithelial cells leads to the formation of a continuous dental lamina in the shape of a horseshoe sinking into the underlying mesenchyme: this is the primitive lamina or plunging wall.
- Formation of the primary dental lamina:
From the primitive dental lamina, the primary dental lamina arises in the lingual or palatal direction. The dental lamina is surrounded by a condensation of ectomesenchymal cells at the level of which epithelial swellings are organized; they respond to the future dental buds.
- Formation of the secondary dental lamina:
It is at the bell stage that the secondary dental lamina responsible for the germs of permanent teeth in humans is formed. One secondary dental lamina is formed per primary dental lamina for each of the temporary germs.
The buds of the 20 successive permanent teeth will come from another extension of the primary lamina, while a posterior extension of the primary dental lamina will give the buds of the three non-successional teeth: the permanent molars.
- Development of the dental organ:
Each condensation of ectomesenchymal cells at the level of which epithelial swellings are organized (future dental buds) will evolve in an identical histological manner whatever its location on this dental lamina until the bell stage. Three stages are usually and arbitrarily described:
• Bud stage:
Between the 7th and 8th week, shortly after the formation of the dental lamina, and from this, small epithelial swellings covering mesenchymal cells regularly and locally become individualized: these are the buds, future organs of the enamel of temporary teeth. Before involuting by cell death (apoptosis), part of this dental lamina will still be capable of forming the buds of replacement teeth (or permanent teeth).
It is noteworthy that replacement teeth begin their morphological development during the odontogenesis of temporary teeth.
• Cup stage:
At the 10th week, the tooth bud becomes depressed in its anterior (mesial) part. The depression progresses from the front to the distal part of the germ. The bud, initially forming a compact epithelial mass, will differentiate into an enamel organ.
It gives four components: the external adamantine epithelium and the internal adamantine epithelium which separate the stellate reticulum and the stratum intermedium.
- Bell stage:
This stage is characterized by the continuation of invagination and especially by the establishment of key stages of the morphogenesis of the dental crown. It will gradually have a differentiation of the different cells of the dental organ into ameloblasts: forming dental enamel, pre-odontoblasts: forming dentin and embryonic pulp.
- A- Bud stage
- B- Young cupule stage
- B’- Mature cupule stage
- C- Bell stadium
- Formation of dental alveoli
From the 8th and 9th week of intrauterine life, the maxillary and mandibular bony trabeculae form two gutters facing the oral cavity.
Later, and around the 4th and 5th month of intrauterine life, transverse bony trabeculae begin to separate the different dental germs
These bony trabeculae will thicken as the dental germs develop, resulting in isolation of the dental region from the vascular-nervous axis and the bottom of the groove will transform into a canal, this is the dental canal.
2- Tooth eruption
2- 1 Definitions
• DENTITION AND DENTURE
Dentition defines the formation and natural emergence of teeth. It constitutes the construction of the dentition, which is the set of teeth.
2-2- DENTAL ERUPTION
Tooth eruption is the driving force behind teething and begins with the formation of the dental lamina until the establishment of adult teeth.
It is a localized, symmetrical and time-programmed process.
It first concerns the temporary teeth and then the permanent teeth. This phenomenon allows the teeth to move up to the dental arch
2-3-Phases of dental eruption:
2-3-1- Passive eruption phase:
- Begins with calcification of the crown, and ends when this is complete.
- The bony apposition, at the level of the cortices, increases the distance between the germ and the basilar edge, but the germ does not rise.
2-3-2 -Pre-functional active eruption phase:
- When the root begins to form, migration towards the arch crest is faster than bone apposition. The appearance of the crown in the oral cavity occurs after fusion of the reduced adamantine epithelium and the buccal epithelium in the attached gingiva.
2-3-3 Functional implementation:
On average ¾ of the root height built:
• 1st stage: the root is not yet fully developed, the apex is widely open.
• 2nd stage: complete apical edification.
- From oral emergence to first contact with the antagonist.
2-3-4- Occlusal adaptation:
- Depending on the relationships established with the opposing teeth
- This is the longest (several years). In fact, axial movements and alveolar growth continue, even after the tooth is put into functional occlusion, but at a much slower rate.
- Mesial drift is also observed accompanying interproximal attrition of the teeth.
- This post-occlusal phase ends when the tooth disappears.
2-4- Biological mechanisms of dental eruption:
- Tooth eruption is a complex growth process involving both the teeth and the surrounding bone tissues.
- It is thus accompanied by multiple tissue modifications such as resorption and apposition of alveolar bone, root growth and development of the desmodont.
- However, the mechanism that governs this phenomenon remains poorly understood but several hypotheses have been put forward.
- In the different hypotheses, this phenomenon can be attributed either to a simple causal agent called “primary driver” or to a combination of agents and we will speak of the “multifactorial theory”.
- There are many theories explaining the mechanism of tooth eruption:
.1 Root formation
- Many authors have attributed the driving role of eruption to root formation.
- Two observations nevertheless qualified this assertion:
– The discovery of the eruption of teeth without roots.
– Normal root formation not followed by eruption. Example: impacted teeth
2-Pulpal and peri-pulpal proliferation
- For some authors, pulp and peripulpal proliferation would be responsible for the axial displacement of the tooth.
- But here too, this theory cannot be accepted since teeth that are depulped or have pulp necrosis continue to erupt.
3-Cellular proliferation of the odontogenic layers:
It involves the cell proliferation of the odontogenic layers, by reducing the pulp volume and therefore increasing the blood pressure in the dental sac. Authors have carried out an experiment with hypotensive agents thus modifying the blood pressure, they were unable to observe any modification in the speed of eruption.
4 Multifactorial design of dental eruption:
None of the above theories has clearly demonstrated its exclusive involvement. It is therefore wise to consider that the phenomenon of dental eruption would be the result of a participation of all factors. We will speak of a multifactorial process.
However, it is necessary to have:
• Mechanism generating forces capable of eroding the tooth.
• Process by which such forces enable eruption through movements through the surrounding tissue.
• Process of maintaining eruption so that the tooth is held in its new position.
• Remodeling of periodontal tissues to maintain the functional integrity of the system
2-5-Chronology of normal eruption:
The chronology and dates of eruption of temporary or permanent teeth present a relatively large variability, linked to various factors such as ethnic origin or sex, without however having real pathological consequences. Thus, the eruption is earlier in girls and in black individuals
2-5-1 – Eruption of temporary teeth
The eruption of primary teeth shows little individual variation. On average, the eruption of primary teeth begins around 8 months with the mandibular central incisors and ends around 30 months with the maxillary second molars.
2-5-2- Eruption of permanent teeth:
In permanent dentition, the variability of eruption dates is greater than in temporary dentition. In particular, greater variability is observed for canines, premolars and second molars, while it is less for incisors and first molars.
The eruption in girls is significantly earlier than in boys by around 6 months, this phenomenon becoming more pronounced during puberty.
There is also a difference between the maxilla and the mandible, the latter presenting a slight advance of eruption.
On average, the eruption of permanent teeth lasts 6 years (except for the third molar), it begins around 6 years with the mandibular central incisors and ends around 12 years with the second molars. The third molars erupt between 18 and 25 years.
the stages of dental arch morphogenesis
Démogé proposed a classification which responds to the clinical concerns of orthodontics, especially interceptive and preventive.
Table: The ten phases of tooth formation according to DEMOGE 1972
- Conclusion
The development of the dental arches involves the participation of several tissues of diverse origins and variable chronology for each element, which is why all the modifications that the dental arch undergoes in relation to the phenomena of dentition remain essential to the harmonious development of the dentition and the establishment of a dental occlusion allowing the various functions incumbent upon it to be ensured.
The dental arches and the bony bases constitute the terrain on which the orthodontist is led to intervene. It is therefore appropriate for the latter to have perfect knowledge of all the phenomena which govern the morphogenesis of these structures.
MORPHOGENESIS OF DENTAL ARCHES
Deep cavities may require root canal treatment.
Dental veneers correct chipped or discolored teeth.
Misaligned teeth can cause uneven wear.
Dental implants preserve the bone structure of the jaw.
Fluoride mouthwashes help prevent cavities.
Decayed baby teeth can affect the position of permanent teeth.
An electric toothbrush cleans hard-to-reach areas more effectively.