The axial or occlusal movement of tooth from its developmental position within the jaw to its functional position in the occlusal plane is known as eruption of teeth.
There are three types of movements:
Permanent teeth with deciduous predecessors also undergo complete movement before they reach the position from which they erupt. As their deciduous predecessors erupt, they move to a more apical position and occupy their own bony crypt. Premolars begin their development lingual to their predecessors at the level of occlusal surface and in same bony crypt. They are situated beneath the divergent roots of deciduous molars. The permanent molars which do not have predecessors also move from the site of their initial differentiation.
ERUPTIVE : There is axial or occlusal movement of tooth from its developmental position within the jaw to its final functional position in the occlusal plane. It is important to recognize that jaw growth is normally occurring while most teeth are erupting, so movement in plane other than axial is superimposed on eruptive movement.
POST - ERUPTIVE : These movements are those that :-
There are three types of movements:
- Pre - Eruptive
- Eruptive
- Post - Eruptive
Permanent teeth with deciduous predecessors also undergo complete movement before they reach the position from which they erupt. As their deciduous predecessors erupt, they move to a more apical position and occupy their own bony crypt. Premolars begin their development lingual to their predecessors at the level of occlusal surface and in same bony crypt. They are situated beneath the divergent roots of deciduous molars. The permanent molars which do not have predecessors also move from the site of their initial differentiation.
ERUPTIVE : There is axial or occlusal movement of tooth from its developmental position within the jaw to its final functional position in the occlusal plane. It is important to recognize that jaw growth is normally occurring while most teeth are erupting, so movement in plane other than axial is superimposed on eruptive movement.
POST - ERUPTIVE : These movements are those that :-
- Maintain the position of the erupted tooth which the jaw continues to grow.
- Compensates for proximal and occlusal wear.
THEORIES OF TOOTH ERUPTION
- Bone Re-modelling
- Root growth
- Vascular pressure
- Periodontal ligament traction
(a) BONE RE-MODELLING :- It supposes that selective deposition and resorption of bone brings eruption. In the experiments, where tooth germ is removed and the follicle is left in the position the eruptive pathway still form in bone. Thus this indicates the dental follicle and not bone as major determinant in tooth eruption.
(b) ROOT GROWTH : Root formation is also unlikely to be the cause of tooth eruption; as the onset of root formation is not synchroneous with onset of axial tooth movement. It causes overall increase in length of tooth that must be accompanied by root growing in the bone of jaw by an increase in jaw length or by crowing moving occlusally.
But it is not accepted. For example, if erupting tooth is prevented from erupting by pinning it to the bone, root growth continues and is surrounded by resorption of bone at base of socket.Thus although it can produce force, root growth can not be translated into eruptive movement unless there is some structure at the base of tooth, capable of withstanding this force but no such structure exists.
Advocates of the root growth theory postulated the existence of a ligament, the cushion - hammock ligament, straddling the base of the socket from one bony wall to the other like a sling. But the hammock ligament is the pulp delineating membrane that runs across the apex of the tooth and has no bony insertion so it can not act as a fixed base.
(c) VASCULAR PRESSURE : It states that there is a higher pressure system either within or around the base of tooth. It is known that teeth move in synchrony with arterial pulsation, so local volume changes can produce limited tooth movement.
Whether such pressure is prime for movement of teeth is debatable because surgical excision of the root and therefore the local vasculature does not prevent tooth eruption.
(d) PERIODONTAL LIGAMENT TRACTION : There is good deal of evidence that eruptive force resides in the dental follicle-periodontal ligament complex. As long as periodontal tissue is available tooth movement occurs. Tissue culture experiments have shown that ligament fibroblast is able to contract a collagen-gel which in turn brings about movement of a disc of root tissue attached to that gel. Thus, there is no doubt that periodontal ligament fibroblasts have the ability to contract and transmit a contractile force to the extra cellular environment and in particular to the collagen fiber bundles in vitro. The entire morphological features exist in vivo to permit similar movement.
In summary, eruptive movement is brought about by a combination of events involving a force initiated by the fibroblasts. This force is transmitted to the extra cellular compartment via fibron exuses and to collagen fiber bundles, which aligned is an appropriate inclination brought about by root formation, bring about tooth movement. These fiber bundles must have the ability to remodel for eruption to continue and interference with this ability affects the eruptive process. The removal of bone to create the eruptive pathway is also dictated by the tissue surrounding the tooth.
CHRONOLOGY OF ERUPTION OF PERMANENT TEETH
QUESTIONS:
Q1: How many types of movements are there in the eruption of teeth?
Ans: Three (Pre-Eruptive, Eruptive and Post-Eruptive)
Q2: Which tooth erupts first in the oral cavity?
Ans: Primary Mandibular Central Incisor
Q3: Which permanent tooth erupts first in the oral cavity?
Ans: Mandibular First Molar.
Q3: Which successor tooth erupts first in the oral cavity?
Ans: Mandibular Central Incisor.
Q4: At what age, primary teeth erupt in the oral cavity?
Ans: At the age of 6 months.
Q5: At what age, Primary Mandibular Central Incisors erupt in the oral cavity?
Ans: 6 months
Q6: At what age, Primary Mandibular Lateral Incisors erupt in the oral cavity?
Ans: 7 months
Q7: At what age, Primary Maxillary Central Incisors erupt in the oral cavity?
Ans: 7 1/2 months
Q8: At what age, Primary Maxillary Lateral Incisors erupt in the oral cavity?
Ans: 9 months
Q9: At what age, Primary Mandibular First Molars erupt in the oral cavity?
Ans: 12 months
Q10: At what age, Primary Maxillary First Molars erupt in the oral cavity?
Ans: 14 months
Q11: At what age, Primary Mandibular Canines erupt in the oral cavity?
Ans: 16 months
Q12: At what age, Primary Maxillary Canines erupt in the oral cavity?
Ans: 18 months
Q13: At what age, Primary Mandibular 2nd Molars erupt in the oral cavity?
Ans: 20 months
Q14: At what age, Primary Maxillary 2nd Molars erupt in the oral cavity?
Ans: 24 months
Q15: At the age of 5 months, how many teeth are present in the oral cavity?
Ans: Nill / 0
Q16: At the age of 6 months, how many teeth are present in oral cavity?
Ans: 2 teeth (Mandibular Central Incisors)
Q17: At the age of 8 months, how many teeth are present in oral cavity?
Ans: 6 teeth ( 4 Mandibular Incisors and 2 Maxillary Central Incisors)
Q18: At the age of 10 months, how many teeth are present in oral cavity?
Ans: 8 teeth ( Incisors)
Q19: At the age of 13 months, how many teeth are present in oral cavity?
Ans: 10 teeth ( 8 Incisors and 2 Mandibular First Molars)
Q20: At the age of 15 months, how many teeth are present in oral cavity?
Ans: 12 teeth ( 8 Incisors and 4 First Molars)
Q21: At the age of 17 months, how many teeth are present in oral cavity?
Ans: 14 teeth (8 Incisors, 4 First Molars and 2 Mandibular Canines)
Q22: At the age of 19 months, how many teeth are present in oral cavity?
Ans: 16 teeth (8 Incisors, 4 First Molars and 4 Canines).
Q23: At the age of 21 months, how many teeth are present in oral cavity?
Ans: 18 teeth (8 Incisors, 4 Canines, 4 First Molars and 2 Second Molars)
Q24: At the age of 25 months, how many teeth are present in oral cavity?
Ans: 20 teeth (8 Incisors, 4 Canines and 8 Molars)
(b) ROOT GROWTH : Root formation is also unlikely to be the cause of tooth eruption; as the onset of root formation is not synchroneous with onset of axial tooth movement. It causes overall increase in length of tooth that must be accompanied by root growing in the bone of jaw by an increase in jaw length or by crowing moving occlusally.
But it is not accepted. For example, if erupting tooth is prevented from erupting by pinning it to the bone, root growth continues and is surrounded by resorption of bone at base of socket.Thus although it can produce force, root growth can not be translated into eruptive movement unless there is some structure at the base of tooth, capable of withstanding this force but no such structure exists.
Advocates of the root growth theory postulated the existence of a ligament, the cushion - hammock ligament, straddling the base of the socket from one bony wall to the other like a sling. But the hammock ligament is the pulp delineating membrane that runs across the apex of the tooth and has no bony insertion so it can not act as a fixed base.
(c) VASCULAR PRESSURE : It states that there is a higher pressure system either within or around the base of tooth. It is known that teeth move in synchrony with arterial pulsation, so local volume changes can produce limited tooth movement.
Whether such pressure is prime for movement of teeth is debatable because surgical excision of the root and therefore the local vasculature does not prevent tooth eruption.
(d) PERIODONTAL LIGAMENT TRACTION : There is good deal of evidence that eruptive force resides in the dental follicle-periodontal ligament complex. As long as periodontal tissue is available tooth movement occurs. Tissue culture experiments have shown that ligament fibroblast is able to contract a collagen-gel which in turn brings about movement of a disc of root tissue attached to that gel. Thus, there is no doubt that periodontal ligament fibroblasts have the ability to contract and transmit a contractile force to the extra cellular environment and in particular to the collagen fiber bundles in vitro. The entire morphological features exist in vivo to permit similar movement.
In summary, eruptive movement is brought about by a combination of events involving a force initiated by the fibroblasts. This force is transmitted to the extra cellular compartment via fibron exuses and to collagen fiber bundles, which aligned is an appropriate inclination brought about by root formation, bring about tooth movement. These fiber bundles must have the ability to remodel for eruption to continue and interference with this ability affects the eruptive process. The removal of bone to create the eruptive pathway is also dictated by the tissue surrounding the tooth.
CHRONOLOGY OF ERUPTION
CHRONOLOGY OF ERUPTION OF PRIMARY TEETH
TEETH
|
ERUPTION
AGE
|
Mandibular Central
Incisor
|
6
Months
|
Mandibular Lateral
Incisor
|
7
Months
|
Maxillary Central
Incisor
|
7
½ Months
|
Maxillary Lateral
Incisor
|
9
Months
|
Mandibular First Molar
|
12
Months
|
Maxillary First Molar
|
14
Months
|
Mandibular Canine
|
16
Months
|
Maxillary Canine
|
18
Months
|
Mandibular 2nd
Molar
|
20
Months
|
Maxillay 2nd
Molar
|
24
Months
|
CHRONOLOGY OF ERUPTION OF PERMANENT TEETH
Teeth
(listed in order of eruption sequence)
|
Eruption time
|
Mandibular
1st Molar
|
6 – 7 Years
|
Maxillary
1st Molar
|
6 – 7 Years
|
Mandibular
Central Incisor
|
6 – 7 Years
|
Maxillary
Central Incisor
|
7 – 8 Years
|
Mandibular
Lateral Incisor
|
7 – 8 Years
|
Maxillary
Lateral Incisor
|
8 – 9 Years
|
Mandibular
Canine
|
9 – 10 Years
|
Maxillary
1st Premolar
|
10 – 11 Years
|
Mandibular
1st Premolar
|
10 – 11 Years
|
Maxillary
2nd Premolar
|
10 – 12 Years
|
Mandibular
2nd Premolar
|
11 – 12 Years
|
Maxillary
Canine
|
11 – 12 Years
|
Mandibular
2nd Molar
|
11 – 12 Years
|
Maxillary
2nd Molar
|
12 – 13 Years
|
Mandibular
3rd Molar
|
17 – 20 Years
|
Maxillary
3rd Molar
|
18 – 20 Years
|
QUESTIONS:
Q1: How many types of movements are there in the eruption of teeth?
Ans: Three (Pre-Eruptive, Eruptive and Post-Eruptive)
Q2: Which tooth erupts first in the oral cavity?
Ans: Primary Mandibular Central Incisor
Q3: Which permanent tooth erupts first in the oral cavity?
Ans: Mandibular First Molar.
Q3: Which successor tooth erupts first in the oral cavity?
Ans: Mandibular Central Incisor.
Q4: At what age, primary teeth erupt in the oral cavity?
Ans: At the age of 6 months.
Q5: At what age, Primary Mandibular Central Incisors erupt in the oral cavity?
Ans: 6 months
Q6: At what age, Primary Mandibular Lateral Incisors erupt in the oral cavity?
Ans: 7 months
Q7: At what age, Primary Maxillary Central Incisors erupt in the oral cavity?
Ans: 7 1/2 months
Q8: At what age, Primary Maxillary Lateral Incisors erupt in the oral cavity?
Ans: 9 months
Q9: At what age, Primary Mandibular First Molars erupt in the oral cavity?
Ans: 12 months
Q10: At what age, Primary Maxillary First Molars erupt in the oral cavity?
Ans: 14 months
Q11: At what age, Primary Mandibular Canines erupt in the oral cavity?
Ans: 16 months
Q12: At what age, Primary Maxillary Canines erupt in the oral cavity?
Ans: 18 months
Q13: At what age, Primary Mandibular 2nd Molars erupt in the oral cavity?
Ans: 20 months
Q14: At what age, Primary Maxillary 2nd Molars erupt in the oral cavity?
Ans: 24 months
Q15: At the age of 5 months, how many teeth are present in the oral cavity?
Ans: Nill / 0
Q16: At the age of 6 months, how many teeth are present in oral cavity?
Ans: 2 teeth (Mandibular Central Incisors)
Q17: At the age of 8 months, how many teeth are present in oral cavity?
Ans: 6 teeth ( 4 Mandibular Incisors and 2 Maxillary Central Incisors)
Q18: At the age of 10 months, how many teeth are present in oral cavity?
Ans: 8 teeth ( Incisors)
Q19: At the age of 13 months, how many teeth are present in oral cavity?
Ans: 10 teeth ( 8 Incisors and 2 Mandibular First Molars)
Q20: At the age of 15 months, how many teeth are present in oral cavity?
Ans: 12 teeth ( 8 Incisors and 4 First Molars)
Q21: At the age of 17 months, how many teeth are present in oral cavity?
Ans: 14 teeth (8 Incisors, 4 First Molars and 2 Mandibular Canines)
Q22: At the age of 19 months, how many teeth are present in oral cavity?
Ans: 16 teeth (8 Incisors, 4 First Molars and 4 Canines).
Q23: At the age of 21 months, how many teeth are present in oral cavity?
Ans: 18 teeth (8 Incisors, 4 Canines, 4 First Molars and 2 Second Molars)
Q24: At the age of 25 months, how many teeth are present in oral cavity?
Ans: 20 teeth (8 Incisors, 4 Canines and 8 Molars)
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