The first permanent molar in children
The immaturity of a permanent tooth on the arch is defined as a physiological dental state before the end of root formation, apical closure, i.e. the establishment of the cemento-dentin junction, and functional occlusion of the tooth.
Immature permanent teeth are present from the mixed dentition (6 years) until the beginning
from the young adult dentition phase (15 years old).
An immature permanent tooth has certain histological, anatomical and physiological characteristics.
I/ Morphogenesis of dental germs:
Human beings are characterized by heterodont-diphyodont dentition, the development of the temporary dentition begins morphologically around the 6th or 7th week of gestation and then quickly, there is partial coexistence of deciduous dental sketches (temporary and permanent).
The development of permanent molars differs from that of other permanent teeth in two specific ways:
- These teeth do not appear at the level of the dental lamina, but from its distal extension or distal to the second temporary molar at the 3rd-4th month, and appear as the ascending branch recedes and the oral cavity expands.
- The buds are said to be monophyseal because they do not have replacement teeth even if a temporary replacement dental lamina appears above the latter without producing a bud, and degenerates.
| First maxillary molar | Mandibular first molar | |
| Onset of coronary calcification | Birth | Birth |
| End of coronary calcification | 3 to 4 years | 2.5 to 3 years |
| Eruption | 6 years old | 6 to 7 years old |
| End of apical calcification | 9 to 10 years old | 9 to 10 years old |
Formation of first permanent molars and eruption time
Odontogenesis is classically described by the succession of various stages: blade, bud, cap and dental bell, terminal differentiation of odontoblasts and ameloblasts, root formation (rhizagenesis) and functional differentiation of cementoblasts, dental eruption.
The permanent tooth develops over several years, from its intraosseous position to its functional position in the oral cavity, passing through several anatomical situations, which can be schematically summarized in four stages as mentioned by Lautrou in 2006.
II/anatomical characteristics
- The first maxillary molar: has:
- 3 roots: a palatal root, a mesio-vestibular root and a disto-vestibular root. Each of the roots contains one or more canals, notably the mesio-vestibular root which often has 2 canals.
- The roots can sometimes be fused.
- A crown whose overall shape is a parallelogram, it is the only one whose palatal face is wider than the vestibular face. This palatal face has a particularity: the Carabelli tubercle.
The crown includes:
- 4 cusps: 2 vestibular cusps and one palatal cusp arranged in a triangle, and a fourth cusp, located disto-lingually.
- An enamel bridge connecting the mesiopalatal cusp and the distovistibular cusp.
Occlusal anatomy of the maxillary first molar
- The first mandibular molar: has:
- A mesial root, which has 2 canals.
- A strongest distal root, which may have 1 or 2 canals.
- The crown has a much wider occlusal table than the upper molar, it includes:
- 5 cusps: 3 buccal and 2 lingual cusps and sometimes an additional mesiolingual cusp.
- This surface is made up of numerous depressions: furrows, pits and cracks.
- The overall shape of the crown is a pentagon or trapezoid.
The mesio-distal diameter is larger than the vestibulo-lingual, and this diameter is the largest
among all the other teeth in the arch.
- Occlusal anatomical characteristics of the immature first permanent molar:
The immature first permanent molar (IPPM) has a complex occlusal surface, not yet worn down by chewing and physiological attrition. This surface is made up of numerous depressions: grooves, pits and fissures which are areas of anatomo-histological adaptation of the enamel surface.
The grooves and pits originate, during their mineralization, from a junction zone and not from a synthesis zone. This union is achieved by coalescence of the enamel prisms. They are deep, narrow and crevices.
Anfractuous grooves are defined by the French National Authority for Health (HAS, 2005) as “grooves that appear deep and narrow on simple clinical examination.” In the case of anfractuous grooves, the cusp sides often have lobes that are very marked by secondary grooves.
Coalescence defects are common and lead to the exposure of dentin. This narrow area, called a fissure, is more permeable. It promotes the accumulation of food debris and bacteria and prevents access for brushing or saliva flushing.
Fortier and Demars (1987) established a classification of pits and fissures into 3 types. These different types of grooves exist and often coexist on the same occlusal surface; their depth and the angle of the walls determine caries susceptibility.
According to the HAS, the main areas of congruence on the enamel surface are:
- The main or intercuspid grooves: located at the intersection of the cusps that they separate;
- Secondary or accessory furrows: furrows descending the cusp slopes which they separate;
- Marginal pits: located at the ends of the main furrows;
- Secondary dimples: located on the path of the main furrows (at their intersection).
III/ physiology of the immature first permanent molar
- Email immaturity
When the tooth erupts into the oral cavity, the enamel is immature and hard, and will benefit
for 2 to 3 years following its post-eruptive maturation.
During this period following eruption, many enamel proteins will disappear in favor of the mineral filler.
Post-eruptive maturation involves the incorporation of calcium, phosphate, and fluoride through demineralization-remineralization cycles. Phosphate, calcium, and fluoride ion exchanges are constantly taking place at the enamel/biofilm interface. This varies depending on the local concentrations of these different ions and the surrounding pH.
Immature enamel consists of 37% mineral phase, 44% aqueous phase and 19% organic matrix.
The porosity of enamel is explained by the microscopic structure and the formation mechanisms of
enamel during amelogenesis:
- At the microscopic level of its structure, the mineral phase of enamel consists of stacked and grouped hydroxyapatites, forming the prisms of enamel.
These crystallites are nested on top of each other, leaving a very small space for the organic matrix at the interface between prisms and interprismatic substance. This arrangement induces intercrystalline spaces, allowing diffusion and aqueous and ion exchanges.
- Due to its construction, enamel has a rough primary surface. During its development, ameloblasts form growth lines called “Retzius striae,” giving the enamel an “onion skin” structure. On the enamel surface, the ends of these striae depress the surface and form fine grooves or perikymatia, a large porous network that disappears over time through erosion or abrasion.
- Dentin immaturity
During dentinogenesis, odontoblasts first secrete primary dentin, from tooth development to rhizagenesis. At the end of root formation, dentin will be secreted throughout the life of the tooth on the arch; this is called secondary dentin. Finally, in the event of physical, chemical, or bacterial aggression, tertiary dentin will be produced (reaction or repair dentin).
During its eruption, the PMPI does not benefit from the presence of secondary dentin for a period of approximately 3 years. This results in a large pulp chamber and volume, and unretracted pulp horns close to the enamel surface.
Furthermore, this dentin is also said to be immature because the secretion of pericanalicular dentin has not yet taken place. The progressive obliteration of the tubules by this pericanalicular dentin and its hypermineralized border has not yet taken place and the canaliculi are mostly open (approximately 80% at the level of the pulp ceiling). The dentin of the DPI is therefore also porous and permeable.
- Pulpo-radicular immaturity:
The roots of the PMPI appear thin and more or less short depending on their stages of development.
dentin walls are thin and fragile.
The pulp cavity (pulp chamber and root canals) is large as a whole and contains a large pulp mass (difficult to remove).
The very wide canal flared in the sense that the apical end is wider than the cervical end (unlike a mature tooth), we say that the canal is blunderbuss.
Finally, it has a wide, gaping apex called an “apical funnel”.
- Cells and fibers:
Immature pulp is a loose connective tissue rich in cells and poor in fiber:
- Odontoblasts: aligned on the predentin, they form the link between pulp and dentin. In the tooth
just eruptive the cytoplasm of the odontoblast occupies the entire length of the tubule.
- Undifferentiated mesenchymal cells, capable of differentiating into neodontoblasts
responsible for the application of Restorative Dentin, during an attack.
- Low in fiber (collagen).
- Defense cells (lymphocytes, macrophages, etc.), ensuring a very high pulp defense potential
important.
- nerves and vessels : The association of nerve fibers and vessels is close, but exceptions exist, particularly in immature teeth. Indeed, the majority of the pulp volume is occupied by connective tissue and the vessels and nerves are essentially separate.
- The first nerve fibers, which originate mainly from the trigeminal nerve, enter the pulp at the beginning of dentin and enamel formation. The pulp nerve network remains immature throughout tooth formation and stabilizes when inter-arch dental contacts are established. This network is mainly made up of sensory fibers.
The sensory nerve fibers (C fibers), which represent about half of the nerve fibers at the apex, gradually lose their myelin sheath, gather in the center of the radicular pulp to form large bundles that run near the blood vessels. These bundles divide in the pulp chamber into cuspal nerves, which gradually branch out as they approach the pulp periphery, to terminate in the acellular layer of Weil, in the form of a dense network called the subodontoblastic nerve plexus or Raschkow plexus, which consists only of unmyelinated nerve endings, its maturity is established shortly after the completion of dental eruption. Therefore, responses to pulp sensitivity tests are inconsistent when these are applied to partially developed teeth.
- The young dental pulp is very richly vascularized with a still immature and voluminous vascular-nervous bundle. Capillary blood flow in the coronal region is approximately twice as great as in the root. Blood supply is mainly regulated by precapillary sphincters and sympathetic innervation. As in other tissues, the volume of microvascularization is much greater than that of the blood circulating in it.
- Physiology of the apical region
The immature tooth is essentially characterized by an apical region not yet formed, this zone
highly vascularized and with intense cellular activity, it directly participates in the eruption of the apical third.
As soon as the crown is completely formed, the formation of the root begins by epithelial proliferation in the underlying connective tissues, proliferation which constitutes the Hertwig sheath, the cells of the internal adamantine epithelium retain an inductive power towards the neighboring connective tissue which continues to differentiate into odontoblasts to develop the root dentin.
The odontoblasts will thus form primary dentin until the desired length is obtained
normal root.
The Hertwig sheath thus participates in the formation of the apical artifice by centripetal horizontal growth and in the elongation of the root, to evolve in a vertical direction.
As soon as the root has reached its final normal length, the Hertwig sheath disintegrates, thus putting the dentine in direct contact with the surrounding connective tissue, by induction on this will lead to the formation of cementoblasts, these develop the primary cementum then the secondary cementum or osteocementum which covers the whole of the root and thus contributes to the formation of the apex.
Even when the root has reached its final length, this apex remains gaping for a period of 3 to 4 years during which the apical funnel will be filled with connective tissue which it will be essential to respect.
It is only in this period that apical maturation will be achieved with the establishment of
the cemento-dentin junction.
Along with dental maturation of course, the structures surrounding the apex will organize themselves:
Establishment of the lamina dura and the dental alveolus, formation of ligament fibers, from the dental sac.
- maturation of the periodontium:
- At the time of eruption there is fusion of the adamantine epithelium and that of the keratinized gingiva. The adamantine epithelium gradually transforms into junctional epithelium, which allows the
maintenance of keratinized tissue on the enamel.
During the occlusal migration of the tooth, gradually, after about ten years, the
marginal crimping of the gingiva reaches the enamel-dentin junction.
- After eruption, the cemento-gingival fibers change orientation, meeting in the gingival corium and the bone margin. Maturation is only effective when the tooth becomes functional.
- Cementum: forms from the interaction between the epithelium of Hertwig’s sheath and the odontoblastic layer via the basement membrane. The formation and maturation of cementum follows two stages of development:
- The pre-functional stage during which a primary distribution for each type of cementum occurs for each root. This phase can last up to 5 years after root development.
- The functional phase of cementum formation occurs only at the end of root elongation
and while the functional orientation of the ligament fibers has already been organized.
- Alveolar bone: Alveolar bone is born, lives, and disappears with the tooth. It is constantly renewed due to physiological migration (or spontaneous movement). This spontaneous tooth movement occurs in a mesial and vertical direction by apposition and destruction phenomena, thanks to bone cells (osteoblasts/osteoclasts).
IV/ The different stages of development of PMPs
The stages of permanent tooth development were established by Nolla in 1960 based on radiological aspects of mineralization, extending from the formation of the dental crypt to the end of root edification.
The tooth erupts at Nolla stage 8. Root formation will be complete approximately 3-4 years after the tooth erupts at Nolla stage 9. This is followed by the closure of the apical orifices and the formation of secondary cementum, which covers the apical part of the root, at Nolla stage 10.
V/Roles of the first permanent molar
- Mastication: shredding-crushing
- Keystone of occlusion
- Determining the vertical dimension
- It ensures the organization of permanent teeth and the growth of the young child.
Conclusion :
The immature first permanent molar constitutes the cornerstone of the masticatory apparatus , it is a true keystone of the dental arch , both at the maxillary and mandibular level. However, because of its precocity of emergence, its posterior position on the arch, the immaturity of the enamel and dentine, its complex occlusal morphology, harmful eating habits and oral hygiene still being learned at this age, make it “a crossroads of all dangers” hence its very early attack by carious disease.
The first permanent molar in children
Untreated cavities can cause painful abscesses.
Untreated cavities can cause painful abscesses.
Dental veneers camouflage imperfections such as stains or spaces.
Misaligned teeth can cause digestive problems.
Dental implants restore chewing function and smile aesthetics.
Fluoride mouthwashes strengthen enamel and prevent cavities.
Decayed baby teeth can affect the health of permanent teeth.
A soft-bristled toothbrush protects enamel and sensitive gums.