Tooth eruption is a developmental process where a tooth goes through the gum and becomes visible in the oral cavity. A new born baby is without teeth for about 6 months of life. It is only at around six months of age that the teeth start erupting into the oral cavity. These teeth are known as baby teeth, milk teeth, deciduous teeth or primary teeth. They remain in the mouth for about 6 years of age and hold the space in the mouth for the permanent teeth.
Human beings are Diphyodont which means that they have two successive sets of dentition in their life. First one is known as Primary dentition and second one is Permanent teeth.
Types of Tooth Eruption
It can be of two types
Active Eruption is the bodily movement of the tooth from its site of development to its functional position in the oral cavity.
Passive Eruption Once the tooth is in the mouth the movement of attached gingiva cervically to expose the entire clinical crown is called as passive eruption.
Patterns of Tooth Movement
Preeruptive tooth movement: It is basically the movement prior to tooth eruption in the mouth. When the primary tooth germ first develops there is ample amount of space between them. But due to their rapid growth, this space is utilized and developing teeth become crowded. So the crowding is relieved by growth of infant’s jaws and eruption position of the teeth
Eruptive tooth movement: It is basically the movement of teeth from its position within the bone of the jaw into the oral cavity.
Post eruptive tooth movement: It occurs mainly after the tooth erupts completely into the oral cavity to maintain the position of the erupted teeth and to compensate for occlusal and proximal wear.
Theories of Tooth Eruption
As the teeth develop and roots form, the teeth start erupting in the oral cavity. Though the process seems simple it has many theories to explain its occurrence. Tooth eruption is a continuous multifactorial process. Various theories are as under
Growth displacement theory- According to this theory, the growing root in the apical direction leads to the eruption of the tooth in the opposite direction.
Tissue fluid pressure theory- It states that the local increase in tissue fluid pressure in the periapical region leads to tooth eruption.
Continued bone formation- This theory supposes that selective resorption and deposition of bone brings about tooth eruption
Contraction of periodontal ligament
Myoblast contraction- This theory proposes that the fibroblasts have some contractile filaments which are in contact with one another and may transmit forces to the collagen bundles in the PDL which in turn bring about the tooth eruption.
Chronology of tooth eruption
Tooth eruption is a dynamic process. The timings for tooth eruption may differ from child to child. Humans have 20 primary teeth and 32 permanent teeth.
Tooth eruption has 3 stages
Primary dentition- The first teeth to erupt in the oral cavity are the lower central incisors. They erupt at the age of 6 months. Next the upper four front teeth erupt. After that all the teeth slowly erupt in the oral cavity until all the 20 teeth are not present. At the age of 2 ½ to 3 years all the primary teeth are in mouth and are retained till the age of 6-7 years.
Mixed dentition period- The period during which both primary and permanent teeth are present in the mouth together is known as the mixed dentition period. The permanent teeth that erupt in place of primary teeth are called as successional teeth. The permanent teeth that erupt posterior to permanent teeth are called as accessional teeth.
Permanent period- This stage begins with the eruption of the permanent second molar at the age of 12 years. The transient malocclusion seen in the mixed dentition period gets corrected and the occlusion is stabilized.
The timings at which a tooth generally erupts into the mouth may vary. Variation of 6-12 months in tooth eruption is considered as normal. If the tooth still didn’t erupt in the oral cavity and erupt after its allotted time interval is known as Delayed eruption.
Hence Delayed eruption maybe defined as the emergence of tooth into the mouth at a time that deviates significantly from its original established time of eruption. Delayed eruption maybe significant concern for children and their parents during the mixed dentition period especially.
There can be several reasons for this delayed eruption of the teeth some of which are listed below
1. Local Causes – include Physical Obstruction which may be due to
a). Supernumerary teeth- are the most common cause for delayed eruption of teeth. Supernumerary teeth are the extra teeth which may form during the tooth development. Mesiodens are the most common supernumerary teeth present between the central incisors. They form a barrier for the eruption of the permanent teeth. These extra teeth may also cause tooth irregularity, displacement, rotation and even failure of eruption of teeth.
b). Gingival Swelling- Severe gingival swelling may act as a mucosal barrier to tooth eruption. Gingival swelling can be due to hormonal (pregnancy or puberty) or hereditary, Vit C def or due to drugs such as Phenytoin and Calcium Channel blockers.
c). Injuries to Primary teeth- Injuries to primary teeth can cause delayed eruption. Injured teeth may fuse with the bone leading to tooth ankylosis. Tooth ankylosis leads to over retention of those teeth and hence interferes with the eruption of the permanent teeth.
d). Tumors (odontogenic and non odontogenic tumors) - Tumors in the oral cavity may lead to delayed eruption of teeth. Regional Odontodysplasia also known as Ghost teeth are also associated with delayed eruption are commonly seen with upper front teeth.
e). Ectopic Eruption- Teeth when erupt away from their normal position is known as ectopic eruption which may cause hindrance for the eruption of permanent teeth.
f). Premature loss of primary teeth- Early loss of primary teeth may lead to delayed eruption of permanent teeth.
g). Arch length deficiency- is the most common cause of crowding and impactions. Arch length deficiency may lead to ectopic eruption which may lead to delayed eruption.
h). X ray radiation- may cause root formation impairment, PDL damage and insufficient mandibular growth leading to delayed tooth eruption. Ankylosis of bone to tooth is most common seen in irradiated patients.
2. Systemic Causes
a). Nutritional deficiency- Delayed eruption is most frequently reported in patients who lack essential nutrients.
b). Endocrine disturbances- may affect the timings of tooth eruption. Most common endocrine disorders associated with delayed eruption are-
c). Hypopituitarism/ dwarfism- Shedding of teeth and eruption of teeth are delayed in dwarf patients. The dental arches are small and cannot accommodate all the teeth.
d). Hypothyroidism & hyperthyroidism- In hypothyroidism patients’ teeth develop late in life whereas in children suffering from hyperthyroidism premature exfoliation of teeth is seen.
e). Vit D Resistant Rickets- Children suffering from Vit D resistant rickets also shows delayed eruption of teeth
f). Preterm Babies – It has been seen that in very low birth weight babies’ maturation of permanent teeth delays.
g). HIV patients- also reported to have delayed eruption of teeth
h). Cerebral palsy- Children suffering from cerebral palsy have unerupted and delayed eruption of teeth.
i). Cleidocranial Dysostosis- is a hereditary skeletal disorder characterized by missing collarbones. Due to missing or partly present collar bones this allows hyper mobility of shoulders including the ability to touch the shoulders together in front of the chest. Bones and joints are underdeveloped. Fontanelles are open and failed to fuse. Supernumerary and multiple un erupted teeth present. Bossing of forehead.
j). Cherubism- is a genetic disorder characterized by bilaterally swelling of cheeks. Premature loss of teeth and delayed eruption of teeth occurs in children suffering from cherubism.