Eruption sequence and timing
The process of the formation of the teeth and their eruption to the functional
position in the mouth involve a period of early development in a cellular state,
followed by a period of formation of the hard tissue of the crown, and then by a
period of root formation which generally coincide with the eruption of the tooth.
A consideration is made of the way on which these processes in the
individual teeth are timed so as to permit the proper arrangement of the
dentition both before and after eruption.
Although the small jaws of the child must accommodate the member of both
dentition from the fetal life until about 7 year this is possible because of the
following factors:
1. While the crowns of the deciduous teeth are forming in the jaws the
permanent teeth are at the tooth germ stage.
2. By the time the crowns of permanent teeth are forming the deciduous teeth
are erupted or erupting.
3. Since there is a period of about six years between the appearance of each of
the permanent molars this allows sufficient time for jaw growth to accommodate
the lengthening of the dental arch.
Schematic representation of mandibular growth, showing the fetal
Mandible superimposed upon the adult mandible.
During the period of eruption of deciduous teeth and their establishment as
the functioning dentition the crowns of the successional permanent teeth, lying
in their crypts, are forming. The 1st permanent molar start to calcify earlier,
about the time of birth, before the beginning of the eruptive tooth movement of
the deciduous teeth. The 2nd permanent molar begins to calcify towards the end
of the 3rd year; and the 3rd molar at around 9 years.
Dental age 6 month
After the crowns of permanent teeth are formed there is an interval of
quiescence, until with the commencement of eruption tooth formation again
becomes active. For, as in the case of the deciduous teeth, root formation does
not properly begin until the teeth start their movement towards the mouth
cavity.
The roots of the permanent teeth are completed two to three years after the
tooth first appears in the mouth.
While the crown of the permanent incisors and canines lie unerupted in the
jaws they are situated lingual to the roots of their deciduous predecessors. The
crowns of the canines, and particularly of the upper canine, are placed at a deeper
level than those of the incisors. Moreover, the crowns of the lateral incisors are
generally in a more lingual position than the other anterior teeth. This facilitates
the packing of the crowns of the permanent teeth into the jaws beneath the much
smaller deciduous incisors and canines.
The crowns of the permanent incisors (gray) lie lingual to the crowns of the primary incisors
(yellow), particularly in the case of the maxillary laterals. Arrows point to the primate spaces
The developing premolar crowns are at first to be found between the roots of
their respective deciduous predecessors, the deciduous molars, but by six years
of age they lie at deeper level in the jaws relative to the deciduous molars, and
beneath the apices of the molar.
Dental age is determined from three characteristics. The first is which teeth
have erupted. The second and third, which are closely related, are the amount of
resorption of the roots of primary teeth and the amount of development of the
permanent teeth.
The permanent teeth tend to erupt in groups, and it is less important to know
the most common eruption sequence than to know the expected timing of these
eruption stages. The stages are used in the calculation of dental age, which is
particularly important during the mixed dentition years.
New born
The mesio-buccal cusp of the 1st permanent molar is calcified. The
developing tooth germ of the permanent incisors, canine, and pre molars lie to
the lingual side of the developing deciduous teeth in the same alveoli but they
have not been begun to undergo calcification. In the upper jaw the developing
teeth lie close beneath the orbital cavity, and the maxillary sinus lies on their
inner side but has not yet grown out word over the teeth.
Dental age 1 year
The occlusal surface of the 1st permanent molar is complete. Calcification has
commenced in the upper permanent central incisor, the lower incisors, and the
canine, and just about to begin in the upper lateral incisor. The ramus of
mandible increase greatly in height and width and attached to the body of
mandible with a more acute angle.
Dental age 3 years
The crowns of permanent incisors are almost complete; that the canine about
two-third completed; and calcification has just commenced in the premolars,
which are embraced by the roots of the deciduous molars. The crown of the 1 st
permanent molars is virtually complete.
Dental age 6 years
The first stage of eruption of the permanent teeth, the transition from the primary
to the permanent dentition at dental age 6, is illustrated in Figure below. The most
common eruption sequence is the eruption of the mandibular central incisor,
closely followed by the mandibular first permanent molar and the maxillary first
permanent molar. These teeth normally erupt at so nearly the same time, however,
that it is quite within normal variation for the first molars to slightly precede the
mandibular central incisors or vice versa.
Usually, the mandibular molar will precede the maxillary molar. The beginning
eruption of this group of teeth characterizes dental age 6.
Dental age 6 years
Dental age 7 years
In the second stage of eruption at dental age 7, the maxillary central incisors
and the mandibular lateral incisors erupt. The maxillary central incisor is usually
a year behind the mandibular central incisor, but erupts simultaneously with the
mandibular lateral incisor. At dental age 7, root formation of the maxillary lateral
incisor is well advanced, but it is still about 1 year from eruption, while the
canines and premolars are still in the stage of crown completion or just at the
beginning of root formation.
Dental age 8 years
Dental age 8 is characterized by the eruption of the maxillary lateral incisors.
After these teeth come into the arch, there is a delay of 2 to 3 years before any
further permanent teeth appear.
Dental age 8 years
Dental age 9, 10 years
Since no teeth are erupting at that time, dental ages’ 9 and 10 must be
distinguished by the extent of resorption of the primary canines and premolars
and the extent of root development of their permanent successors. At dental age
9, the primary canines, first molars, and second molars are present.
Approximately one third of the root of the mandibular canine and the
mandibular first premolar is completed. Root development is just beginning, if it
has started at all, on the mandibular second premolar. In the maxillary arch, root
development has begun on the first premolar but is just beginning, if it is present
at all, on both the canine and the second premolar.
Dental age 10 is characterized by a greater amount of both root resorption of
the primary canines and molars, and root development of their permanent
successors. At dental age 10, approximately one half of the roots of the
mandibular canine and mandibular first premolar have been completed; nearly
half the root of the upper first premolar is complete; and there is significant root
development of the mandibular second premolar, maxillary canine, and maxillary
second premolar.
Teeth usually emerge when three fourths of their roots are completed.24 Thus
a signal that a tooth should be appearing in the mouth is root development
approaching this level. It takes 2 to 3 years for roots to be completed after a tooth
has erupted into occlusion. Another indicator of dental age 10, therefore, would
be
completion of the roots of the mandibular incisor teeth and near completion of
the roots of the maxillary laterals. By dental age 11, the roots of all incisors and
first permanent molars should be well completed.
dental age 9 years
Dental age 11 years
Dental age 11 is characterized by the eruption of another group of teeth: the
mandibular canine, mandibular first premolar, and maxillary first premolar,
which all erupt more or less simultaneously. In the mandibular arch, the
mandibular canine most often appears just ahead of the first premolar, but the
similarity in the time of eruption, not the most frequent sequence, is the important
point. In the maxillary arch, on the other hand, the first premolar usually erupts
well ahead of the canine. At dental age 11, the only remaining primary teeth are
the maxillary canine and second molar, and the mandibular second molar.
Dental age 11 years
Dental age 12 years
At dental age 12, the remaining succedaneous permanent teeth erupt.
Succedaneous refers to permanent teeth that replace primary predecessors; thus a
canine is a succedaneous tooth, whereas a first molar is not. In addition, at age 12
the second permanent molars in both arches are nearing eruption. The
succedaneous teeth complete their eruption before the emergence of the second
molars in most but by no means all normal children. Although mineralization
often begins later, it is usually possible to note the early beginnings of the third
molars by age 12.
dental age 12 years
Dental age 13, 14, 15 years
Dental ages 13, 14, and 15 are characterized by the extent of completion of the
roots of permanent teeth. By dental age 15, if a t h i rd molar is going to form, it
should be apparent on the radiographs, and the roots of all other permanent teeth
should be complete.
Dental age 15 years
Like all other developmental ages, dental age correlates with chronologic age
but the correlation for dental age is one of the weakest. In other words, the teeth
erupt with a considerable degree of variability from the chronologic age
standards.
It remains true, however, that the teeth erupt in the stages described above. A
child who has precocious dental development might have the mandibular central
incisors and first molars erupt at age 5 and could reach dental age 12 by
chronologic age 10. A child with slow dental development might not reach dental
age 12 until chronologic age 14.
A change in the sequence of eruption is a much more reliable sign of a
disturbance in normal development than a generalized delay or acceleration.
The more a tooth deviates from its expected position in the sequence, the greater
the likelihood of some sort of problem. For example, a delay in eruption of
maxillary canines to age 14 is within normal variation if the second premolars
are also delayed, but if the second premolars have erupted at age 12 and the
canines have not, something is probably wrong.