Developmeent of dentition / for orthodontists by Almuzian

M. Almuzian, 2016 John RadcliffeHospital/ Oxford 0
By
Dr. Mohammed Almuzian (Mo)
For inquires please email me at: dr_muzian@hotmail.com

Table of Contents
EMBRYOLOGY OF TEETH ....................................................................................2
GENETIC CONTROL OF THE TOOTH DEVELOPMENT................................2
PRENATAL TOOTH FORMATION........................................................................3
POSTNATAL DEVELOPMENT OF THE DENTITION .......................................4
EDENTULOUS AND PRE-ERUPTIVE STAGES...................................................7
ERUPTION OF DECIDUOUS DENTITION (EARLY PRIMARY
DENTITION) ............................................................................................................ 10
FULL AND FUNCTIONAL PRIMARY DENTITION ........................................ 11
MIXED DENTITION ............................................................................................... 13
FUNCTIONAL PERMANENT DENTITION (FULL PERMANENT
DENTITION) ............................................................................................................ 15
CHANGES IN THE PERMANENT DENTITION INTO ADULTHOOD......... 18
POST-ERUPTIVE MOVEMENT........................................................................... 20
DENTAL MATURATION OR DENTAL DEVELOPMENTAL AGE.......................... 21
APPLICATION OF DENTAL MATURATION.......................................................... 22
DEMIRJIAN METHOD.............................................................................................. 23

Embryology of teeth
The prenatal development of the dentition starts at 4-6 week of IU life. Upper
anterior teeth form from the frontonasal process; maxillary posterior teeth develop
from maxillary process of the first pharyngeal arch while all mandibular teeth
originate from mandibular processes of the first pharyngeal arch, these include
primary and permanent teeth. The basic histology of tooth development suggests that
dental tissues derive from two principle cell types: the oral ectoderm gives rise to
enaml, and the neural ectomesenchymal cells of the first branchial arch contributes to
the formation of of all remaining tooth structures including dentine, pulp tissue,
cementum and periodontal ligament (Sadler, 2011, Sperber et al., 2001).
Genetic control of the tooth development
There are two main types of genes that participate in tooth formation. Firstly, the
signaling genes, which initiate tooth development such as s Pax; Msx; Barx and Axin
which present in the oral ectoderm cells. Secondly, the morpho-genes, which
determine tooth morphology such as SHH, fibroblast growth factors and bone
morphogenetic protein, which present in the neural crest cells. Some genes might be
present in both ecto-mesenchymal and oral epithelial layers and provide a signaling
and morphogenetic control (Maas and Bei, 1997, Ruch, 1995, Sarkar et al., 2000,
Cobourne and Sharpe, 2003). But what is the evidence?
The genetic interaction was proven by a series of recombination experiments that
carried out by Prof. Lumsden at Guys Dental Hospital in the 1988 (Lumsden, 1988).
Prof. Lumsden demonstrated that: tooth development occurs when the oral epithelium
was combined with caudal ectomesnchymal cells (neural crest explanted from the
trunk level) or cranial neural ectomesnchymal cells (neural crest explanted from the
cranial level) but if limb epithelium was combined with any, no teeth formed.
Recombination experiments also suggested the dominance of neural cress cells in the
specification of tooth shape. For example, recombining incisor neural crest cells with
molar epithelium results in the formation of an incisor tooth. Similarly, recombining

molar neural crest cells with incisor epithelium produces a molariform tooth. To sum
up, the recombination experiments demonstrated for the first time that oral epithelium
is essential for initiation of tooth formation while neural cress cells are essential in the
specification of tooth shape.
Prenatal tooth formation
Tooth development consists of six main phases (Fehrenbach and Popowics, 2015,
Ahmed, 2011). The cell interaction and differentiation in these stages is: (1) well-
programmed: i.e. each stage should is under the control of genetic interaction, (2)
sequential: i.e. each stage follow its ancestry stage, and (3) reciprocal: i.e. the
inductive tissue activate the target tissue which in turn activate the differentiation of
its inductive tissue and so on (Thesleff, 2000).
During the initiation stage, development of the deciduous dentition begins at around
4-6 weeks with the formation of a continuous horseshoe-shaped band of thickened
epithelium called oral epithelium, around the lateral margins of the primitive oral
cavity. The free margin of oral epithelium consists of two parts: outer process or
vestibular lamina which deepens to form the oral vestibule that demarcates the
cheeks and lips from the tooth-bearing regions, while the inner process or dental
lamina develops teeth and their supporting structures. Through the bud stage (9th
week of IU life), the dental lamina invaginates into the underlying mesenchyme to
form the tooth bud. The tooth bud give rises to enamel organ and dental lamina of
permanent teeth with the exception of the dental lamina of permanent molars that
develop directly from oral epithelium. The enamel organ consists of two layers: outer
and inner enamel epithelium. At 11th week of IU life, immediately below the inner
enamel epithelium, dental papilla is formed by localized condensation of neural
crest-derived ectomesenchymal cells, the early cap stage. Then, the dental papilla
extends laterally around the enamel organ to form the dental follicle. Enamel organ,
dental papilla and dental follicle are collectively called tooth germ which give rises
to all structures that make up the mature tooth and its associate structures. In the late

cap stage (13th week of IU life), the dental lamina of permanent teeth separates and
the tooth germ fold more (Fehrenbach and Popowics, 2015, Ahmed, 2011).
At the start of the 14th week of IU life (early bell stage), the inner enamel epithelium
grow in size and activate adjacent cells of the dental papilla which differentiate into
odontoblasts that lay down predentine. The first layer of predentine reciprocally acts
as a signal to the overlying inner enamel epithelial cells to differentiate into
ameloblasts and begin secreting the enamel matrix; enamel matrix secretion induces
the conversion of predentine into calcified dentine. This process spread along the
whole crown and result in the formation of calcified crown. Later one, tooth
development enters the late bell stage (16th week of IU life) when cells of the inner
enamel epithelium are confluent with the outer enamel epithelial cells, at the cervical
loop. Growth of these cells in an apical direction forms a skirt-like sheet called
Hertwig’s epithelial root sheath, which maps out the future root morphology of the
developing tooth. Degeneration of this sheath leads to exposure of the dental follicle
to the newly formed enamel that in turn activate the cells of the dental follicle to
produce the alveolar bone and collagen fibres of the preriodontium. At the same time,
Hertwig’s epithelial root sheath activates the underlying dental lamina to secret root
predentine that reciprocally initiates the differentiation of Hertwig’s root sheath into
cementoblasts. The latter calcify to form cementum, which again activate the
conversion of root predentine into dentine. This process continues along the root and
believed to be one of the theories for tooth eruption (Fehrenbach and Popowics, 2015,
Ahmed, 2011).
Dental Anomalies
Stages of Tooth Development and Their Relation to Dental Anomalies
1. Dental Lamina Formation
Migration neural crest cells (ectomesenchyme) into branchial arches
 Anodontia (associated with ectodermal dysplasia)
 Duplication of dental arches

2. Initiation and Proliferation
Induction of ectoderm by ectomesenchyme
 Oligodontia
 Supernumeraries
 Gemination/Fusion
 Compound Odontome
3. Histodifferentiation
 Complex Odontome
4. Morphodifferentiation
 Macro/Microdontia
 Dens Invaginatus (Dens-in-dente)
 Dens Evaginatus
 Taurodontism
 Hutchinson’s incisor / Mulberry molar
 Talon cusp
5. Apposition
Organic matrix apposition and primary mineralisation stage
 Dentinogenesis imperfecta
 Dentinal dysplasia
 Amelogenesis imperfecta (hypoplastic)
 Enamel hypoplasia
6. Calcification
 Amelogenesis imperfecta (hypomineralisation)
 Fluorosis
7. Maturation
Removal of water and enamel proteins
 Amelogenesis imperfecta (hypomineralisation)
 Fluorosis
8. Eruption Stage and Root Development

 Premature, delayed, ectopic eruption
 Transposition
 Impaction
Postnatal development of the dentition
According to Richardson (Richardson, 1999a), the postnatal development of the
dentition consists of 6 stages: Edentulous, pre-eruptive, early primary dentition, late
primary dentition, mixed dentition and full permanent dentition stage.

Edentulous and pre-eruptive stages
The normal features for edentulous stage, which occurs during the first six months
after birth, are 10 maxillary and 10 mandibular gum pads representing the teeth
forming below, well-developed grooves distal to the canine segments called lateral
sulci, and dental or gingival groove, are a horizontal groove on the palatal side
separated The alveolar processes from the palate. At this stage, there is considerable
variation in the antero-posterior relationships of the jaws but assessment is difficult,
as the temperomandibular joints are not fully formed yet. Any parental concern
regarding jaw relationships should be delayed, except if there is an airway risk as in in
Pier Robin Syndrome, as there is no way to predict future relationship (Heaf et al.,
1982). Occasionally, on the alveolar mucosa, small whitish nodules may appear and
often called Epstein’s pearls or Bohn’s nodules. They are about 2-3 mms in diameter,
contain keratin and they tend to occur on the midline of the palate or on the alveolar
gum pads. Parents should be reassured that they will spontaneously burst and resolve
(Cataldo and Berkman, 1968).
Another abnormality, that might be present in the edentulous stage, is natal and
neonatal teeth. The latter erupt during the first 30 days after birth while the former are
that group of teeth present at the birth. Some of these teeth are an actual prematurely
erupted primary teeth while other are supernumerary teeth. The prevalence is 1:2ooo-
3000 baby (Chow, 1980), more in males than counterpart, and more common in
American Indian and Amish group proposing a genetic and racial background (Cunha
et al., 2001). Ironically, in many African tribes, children born with natal teeth were
executed after birth as they were thought to bring bad luck to the tribe (Bodenhoff and
Gorlin, 1963)! Possible aetiologies are genetic factors particularly among Amish
group & association with certain syndrome and/or intra-uterine environmental factors
for example teratogen ,i nfection, malnutrition including hypo-vitaminosis or trauma
(RTa et al., 2002).
Clinically, natal and neonatal teeth may present with swelling of the gum tissue with
an unerupted but palpable tooth, partially erupted or completely erupted with little or

no root. Neonatal teeth may develop some complications such as ainful bitten or
bleeding nipples (Cunha et al., 2001), Riga-Fede disease (trauma to the tip or
undersurface of the tongue) (Buchanan and Jenkins, 1997) or rarely associated with
risk of inhalation or swallowing (Cunha et al., 2001). If these problems develop, then
suggested management should start by consulting paedodontist and some and
palliative treatment using local analgesia. A radiographical evaluation to determine
whether the teeth are normal primary or supernumerary teeth is recommended.
Treatment options could be conservative such as grinding or smoothing sharp edges
of the tooth, composite resin over the sharp edge or changing feeding technique to
reduce nipple trauma. Topical fluoride application should be prescribed if the plan is
to maintain the tooth. Non-conservative treatment include extraction, however it is
important to provide vitamin K supplement before extraction as neonate under the age
of 10 days has very low level of clotting factors and has high risk for bleeding (Cunha
et al., 2001).
Before primary teeth erupt (Pre-eruptive phase), many signs and symptoms related to
teething, develop. A great review paper about teething was published in the British
dental journal by Dr. McIntyre from Dundee (McIntyre and McIntyre, 2002). From
this paper we can conclude that children during teething phase usually suffer general
irritability, malaise, pain, disturbed sleep, bowel upset, loss of appetite and alteration
in volume of fluid intake. Other symptoms are facial flushing (Le Feu Des Dents),
circumoral rash and sialorhoea (Drooling). Children try to rub their ear and gum with
an increase appetite to bite and suck objects. Intraorally, inflammation of the mucous
membrane overlying the tooth possibly with small bleeding might be noticed. As
treatment for teething problem, lancing, which was introduced by Dr. Paré in the 16th
century, was the historical method to treat teething. The procedure involves two
incisions of the tissue overlying the ‘erupting’ tooth.

Teething babies love to feel pressure on their gums because it helps distract their
brain from the sensation of teething pain. Applying pressure can be done using hard
or chilled objects such as:
 Hard sugar-free teething rusks or bread-sticks
 Teething rings (chilled)
 Cucumber (peeled)
 Frozen items (anything from ice cubes to frozen bagels, frozen banana, sliced fruit,
pretzels, vegetables, ice cubes or even frozen pacifier!)
 Rub gums with clean finger, cool spoon, wet gauze
 In sever cases, topical medication or even over-the-counter painkiller like paracetamol
is used.
At the end the pre-eruptive phase, teeth start to appear and there are many theories on
how the eruptive mechanism is generated. One of the theories is the genetic theory;
many genes were found to be in control of eruption process but are defective in
certain disorders and syndromes such as cleidocranial dysplasia leading to delay or no
eruption (impaction). Some believe that eruption’s force comes from the follicle,
which probably has many cytokines and growth factors (Follicular theory). Removal
of the dental follicle results in complete cessation of eruption but if a silicone replica
of a tooth is used to replace a normal tooth during its development, eruption still
occurs as long as the follicle remains intact (Cahill and Marks, 1980).
Other assumed that crown moves occlusally as a result of root growth, however, root
elongation cannot be expected to move a tooth in three-dimensional space (Marks and
Schroeder, 1996). Similarly, formation of bone apical to developing teeth has long
been proposed as one mechanism for eruption (alveolar bone growth theory). There is
no doubt that bone forms in these sites, but bone formation per se is not sufficient for
tooth eruption either. A good example to illustrate this is the presence of an unerupted
dentition in osteopetrotic mutations in which bone formation is nearly normal or
elevated and bone resorption greatly reduced (Marks and Schroeder, 1996).
Moreover, a good evidence suggests that periodontal ligament fibroblasts are capable

of generating contractile forces, pulling the tooth in an occlusal direction (periodontal
activity theory), however, teeth still erupt when the periodontal ligament is disrupted
(Marks and Schroeder, 1996). The last theory in the list is the Hydrostatic forces
theory. It states that forces, which are generated either within the pulp or by the apical
vasculature, are responsible for pushing the tooth in an occlusal direction.
Nevertheless, teeth still erupt when their pulp is removed, and hypertensive drugs
seem to have no effect on eruption (Sutton and Graze, 1985).
Eruption of deciduous dentition (Early primary dentition)
Generally, the first deciduous tooth erupts between the age of 6 and 12 months, still,
all deciduous teeth should be erupted at 3 years. The conventional orders of eruption
are central incisors, lateral incisors, first molars, canines and finally second molars.
Generally, mandibular teeth tend to erupt before maxillary teeth and there is no
gender dominance for eruption date but times can vary up to six months. Root
formation completes 12-18 months after eruption. During eruption the alveolar bone
becomes progressively more developed, there is a small increase in vertical
dimensions, antero-posterior and transverse dimensions as the teeth progressively
erupt, and after eruption the arches change very little until eruption of the permanent
teeth (Richardson, 1999a, Richardson, 1999b).
Prior to tooth’s eruption, a translucent bluish cyst may appear so-called eruption cyst.
There is a gender predilection; male to female ratio is 2:1; they most commonly occur
over primary molars and formed by an accumulation of tissue fluid within the dental
follicle. The cyst requires no intervention as it may spontaneously burst on eruption
but parents may concern, especially if it becomes painful and inflamed, and in this
case it might need surgical excision (Bodner et al., 2005).

Full and functional primary dentition
At 3 years of age, full primary dentition completed. The Ideal deciduous dentition has
six main features (Richardson, 1999a, Richardson, 1999b) as mentioned in table
below.
 Semi-circular arch form
 Incisor spacing
 Positive overjet and overbite;
 Class I canine relationship
 Anthropoid (Primate) spaces. These spaces are located mesial to the maxillary canine
and distal to the mandibular one, they are important for the accommodation of
permanent teeth and parents should be informed of this if concerned.
 Flush or medial step terminal plane molar relationship.
The question now is, does a normal deciduous dentition exist and can a future
malocclusion be predicted from the deciduous dentition?
Foster and Hamilton studied the complete deciduous dentitions of 100 children aged 3
years (Foster and Hamilton, 1969a). Their main finding was that there was not a
single child within this sample that had the six main features at one point. The
greatest variation was seen in the incisor relationship, with only a fifth of children
having a normal overbite, although, almost three-quarters having some increase in the
overjet. The presence of primate spaces was the most constant finding and
approximately one-third of the sample had spacing between all incisors. Furthermore,
around one third to half of the children had second deciduous molars that were flush
in the terminal plane and this is close to findings of other studies (Nanda et al., 1973,
Baume, 1950, Arya et al., 1973). Baume (Baume, 1950) found that 60% of terminal
molar relationship in primary teeth are distal step, 30% are flush and only 10% have
mesial step relationship, however no treatment is indicated at this stage, as growth is
unpredictable.

An answer to the second section of the question is that there is wide individual
variation in occlusal development and predicting a malocclusion in the permanent
dentition, based upon an established deciduous dentition, is difficult. Unilateral
crossbite, anterior open bite and an increased overjet associated with a digit-sucking
habit will usually spontaneously improve, if cessation of the habit occurs before the
mixed dentition is established. However, in the absence of a digit-sucking habit, a
markedly increased or reverse overjet will give a fairly accurate prognosis for the
incisor relationship in the permanent dentition (Larsson, 1994). Additionally, parents
may express concern about developmental incisor spacing in primary dentition but
they should be reassured that this feature is not only developmentally correct but also
important to accommodate the permanent teeth. Leighton 1971 (Leighton, 1970)
showed that approximately, 70% and 50% of children might develop future crowding
if the spacing is >0mm and 1-3, respectively. But, then there will be a little chance for
crowding if the spacing is equal or more than 6mm.
Once primary dentition is complete, between the ages of three and six years, three
changes occur: First, non-carious tooth losses (attrition and/or erosion), which have
the effect of shortening the heights of the incisors, followed by forward movement of
the mandible, the net result is worn teeth that occlude edge to edge. Parents may be
concerned about this but they should be reassured. The second occlusal changes that
take places is the increase in intercanine width which causes either incisor spacing or
increasing of the existent spacing (Richardson, 1999a). The last change is at radicular
level, where roots start to resorb as a first stage for exfoliation. The resorption process
involved is not constant; there are episodes of resorption alternating with periods of
repair. There are four causes of exfoliation of the primary dentition similar to the
theories for tooth eruption (Cahill and Marks, 1980, Marks and Schroeder, 1996) as
mentioned in the table below.

Cementoclastic activity
of permanent teeth
The erupting permanent teeth exert pressure on the
surrounding bone, causing the differentiation of osteoclasts.
These in turn resorb the roots of the primary teeth
Follicular effect of
permanent teeth
1. Where teeth have been experimentally wired to prevent
eruption, bone resorption has continued leading to cystic
cavities. It appears therefore that resorption is the rate-
limiting step and is signalled for by the follicle of the
erupting tooth
Alveolar bone growth Continued growth of the alveolar bone results in loss of
structural support of the deciduous teeth
Force of mastication Increased masticatory forces on the weakened teeth, causes
increased compression of the periodontal ligament and
encourages resorption of primary teeth and alveolar bone
Mixed dentition
By the age of 6, primary teeth start their retirement and exfoliate. The eruption
sequence can be variable. However in the upper jaw the normal sequence of eruption
is 61243578 while in the lower jaw, it follow 16234578 sequences however variation
of 1 year in eruption timing is considered normal.
The first permanent tooth to erupt is the first permanent molar eruption and largely,
30% of First permanent molar erupt in 1/2 unit class II relationship, 10% in class I
and 60% in full unit class II molar relationship (Baume, 1950). The question now,
why classes I molar relationship in late permanent dentition is around 55%? How
these molar relationships change? There are several scenarios (Richardson, 1999a).
The first one called‘’ early mechanism’’ which states that a lower first permanent
molar pushes primary molars forward to occupy the primate space and so class I
molar relationship is generated. However, the upper first permanent molar cannot

drive upper primary molars into primate space because the latter is mesial to upper
primary canine and far away from upper first permanent molar. The second theory
called late mechanism in which normal class I relationship is achieved after
exfoliation of primary molars and via utilisation of the Leeway space. The last
scenario for the potential correction of molar relationship in permanent dentition is
the differential jaw growth mechanism. Looking at Scammon growth curve, it could
be decided that from the age of 10 or mid mixed dentition, mandibular growth rate
(growth speed) become higher than that of maxilla, this might result in correction of
molar relationship. Conversely, a recent study by Barros in 2015 states that mesial
and distal steps molar relationship produce stable relationships of the permanent first
molars as the latter are locked by occlusion (Barros et al., 2015).
As a result, the presence of mesial step molar relationship in primary dentition is
associated with 15% of class III, 5% of class II and 80% of class I molar relationship
in permanent dentition. On the other hand, the presence of flash terminal plane molar
relationship is associated with 45% of class II molar relationship in permanent
dentition (Bishara et al., 1988), while in distal step relationship, half of the cases will
develop class II molar relationship in permanents dentition Bishara et al.,
1988)(Baccetti et al., 1997). If add all these together we will find the exact prevalence
of class I, II and III in Caucasian (Foster, 1974).
The second group of permanent teeth to erupt is upper and lower incisors at
approximately 6 years. When upper and lower central incisors erupt, they essentially
use up all the spacing between the primary incisors, with the eruption of the lateral
incisors at the age of 7-8 years, there is an average of 5 mm of space deficiency in the
lower arch and 6mm in the upper arch, this developmental space deficiency called the
incisor liability. Parents should be reassured that this will improve in most of the
cases. But how? The extra space comes from three sources: transverse growth of the
arch, which can provide up to 1-2 mms of space, permanent incisors eruption in
proclined position and this gives another 1-2 mms of extra space and finally the uses
of primate space, which provide the final 2mm. However, if the primate space was
already burn by mesial movement of buccal segments, then incisor crowding might

develop (Moorrees and Chadha, 1965). Another developmental abnormality during
early mixed dentition is the physiological diastema, which is caused by pressure from
the developing permanent canines. Parents should be reassured that this situation
generally self corrects. A final common developmental abnormality during early
mixed dentition is transient anterior open bite this is mainly due to eruption of the
incisors as they approach the occlusal plane and it is spontaneously corrected without
any treatment unless sucking habit prevent full eruption of incisors.
Functional permanent dentition (Full permanent dentition)
Late mixed or early permanent dentition characterize by the eruption of canines and
premolars. Unlike the anterior teeth the permanent premolars are smaller than the
primary teeth they replace, in particular the second premolars. This extra spaces
known collectively as the leeway space or E space. The reason why it is named E-
space because most of the space is achieved via the differential mesio-distal
dimension between second permanent premolars and second primary molars, while
replacing first primary molar in fact add negligible space to the Leeway. Favorable
development of canines and premolars depends upon favorable eruption sequence,
good tooth arch size ratio, and attainment of a class I molar relationship with minimal
loss of space for canines and favorable transverse relationship between the maxillary
and mandibular alveolar processes. (Proffit et al., 2014).
The sequence of eruption of canines and premolars are variable and they tend to erupt
earlier if the deciduous molars are removed earlier, providing space loss is not so
great to have caused an impaction. In the lower buccal segment, the first tooth to erupt
is either the lower 1st premolar or canine while lower 2nd premolar usually erupts next
but occasionally its eruption is late even after the 2nd permanent molar. In the
maxillary buccal segments, the 1st premolar erupts first followed by the canine and 2nd
premolar. The maxillary canine has the longest eruption pathway and potentially has
more eruptive problems associated with it; Ericson and Kurol recommend annual
inspection and palpation of maxillary canines from the age of 8 years, in order to
intercept if necessary (Ericson and Kurol, 1986). The final stage of permanent

dentition development involves the eruption of 2nd molars between the age of 12-14
years while the third molar eruption is highly variable but is quoted to erupt between
16-20 years or even at 40s (Richardson, 1999a).
In general, the ideal features of permanent occlusion are:
 Ideal static occlusion (Andrew’s six keys)
 Mutually protected functional occlusion.
 The upper canine occludes in the embrasure between the lower permanent canine and
the first premolar.
 The lower incisors should occlude with the cingulum plateau of the upper incisors
 The overbite is about a third of the height of the lower incisor crowns
 The overjet is approximately 2mm.
 In the full dentition the upper buccal segments are tilted slightly outwards and the
lower buccal segments slightly lingually (Curve of Monson).
 The occlusal plane has a distinct upward curve anteriorly (curve of Spee).
Static occlusion is the relationship between the maxillary and mandibular teeth when
the teeth are brought to maximum intercuspation. The ideal static occlusion should
have Andrews’s six keys of occlusion. Andrews (1972) have described keys for an
ideal occlusion based on his study of 120 casts of non-orthodontics models; compared
to 1150 post-treatment study casts that were presented at the American Association of
Orthodontists (Andrews, 1972). Andrews’s six keys are:
1. Class I molar relationship which has two conditions: firstly, the distal surface of the
distal marginal ridge of the upper first molar contacts and occludes with the mesial
surface of the mesial marginal ridge of the lower second molar and secondly, the
mesiobuccal cusp of the upper first permanent molar occlude on the mesiobuccal
groove the lower first molar.
2. Crown Angulation (Tip): In normally occluded teeth the gingival portion of the long
axis of each crown is distal to the occlusal portion of that axis. The degree of tip
varies with each tooth type.

3. Crown Inclination (Torque): This means that always the roots is buccal or labial to the
crown except in upper incisors where the crown is labial to the gingival portion.
4. Rotation: Teeth should be free of undesirable rotations.
5. No spacing
6. Flat curve of Spee or no deeper tham 1.5mm
A seventh key was added by Bennett and McLaughlin (1993) which enforce the
importance of normal tooth-size discrepancies (McLaughlin and Bennett, 2003). With
regard to Dynamic occlusion, Roth stated that an ideal occlusion should function well
(Roth, 1976). His keys for ideal functional occlusion are:
 ICP coincide with RCP
 Presence of mutual protection occlusion:
 Canine guidance or group function
 Incisor guidance
 Upper teeth should overlap lower teeth
 Cusp/fossa lingually
 Cusp/ embrasure buccally
 Teeth should bite along their LA
Mutual protection occlusion is thought to be achieved in the presence of:
1. ICP (or centric occlusion, CO) coincident with the retruded contact position (RCP) (or
centric relation, CR) but with some limited freedom for the mandible to move slightly
forwards in the sagittal and horizontal planes from ICP.
2. An immediate and permanent posterior dis-occlusion in lateral and protrusive contact
with no associated non-working side interferences (tooth contacts); this is achieved by
the presence of canine guidance or group function in lateral excursion and incisal
guidance in protrusion. Thus, the anterior teeth protect the posteriors;
3. Multiple, simultaneous and bilateral contacts of the posterior teeth in intercuspal
position (ICP) with the incisor teeth slightly out of contact; thus, the posterior teeth
protect the anterior.

There are many theories behind functional occlusion similar to the Apollo Moon
Flags myth! It has frequently been proposed that the following problems can result if
Roth functional keys are absent for example:
 Mandibular dysfunction and Bruxism, However a strong evidences by Egermark-
Erikson et al (1983) shows no evidence as most people have nonfunctional occlusion
but not all develop TMD or Bruxsim (Egermark-Eriksson et al., 1983).
 Thirdly, it was claimed that non-functional occlusion is a source for periodontal
disease but again there is very little work to support this idea except in Thilander
study which is an experimental study on dogs and can not rely on it (Ericsson and
Thilander, 1978).
 The last claim is that in non-functional occlusion, teeth positions are unstable and
they are subjected to high risk of relapse however there is weak supporting evidence.
Changes in the permanent dentition into adulthood
These changes include:
1. Slight increase in mandibular prognathism.
2. Reduction of the overbite with age.
3. Increase in the interincisal angle.
4. Arch width (KNOTT, 1972, Carter and McNamara Jr, 1998): The arch width at
intercanine increased after eruption of primary teeth (1-2mm) followed by a period of
little changes then another increase during mixed dentition (3mm) followed by small
increase in intercanine width during permanent dentition. Growth posteriorly provides
space for the permanent molars, and considerable appositional vertical growth occurs
to maintain the relationship of the arches during vertical facial growth. However
regarding the arch width measured at intermolar are, between the ages of 3 and 18
years an increase of 2 in LA and 4 in UA mm takes place but for clinical purposes
arch width is largely established by the late mixed dentition.
5. Arch circumference: It is determined by measuring around the buccal cusps and
incisal edges of the teeth to the distal aspect of the second deciduous molars or second

premolars. There is little change in the maxillary arch with growth. The mandibular
circumference decreases by about 4mm because of the Leeway space utilisation
(Bishara et al., 1996).
6. Late lower incisor crowding (tertiary crowding) (Richardson, 1999b, Bishara et al.,
1996, Richardson, 1994): Apart from third molar development the most noticeable
change is an increase in crowding between the ages of 15 - 20 years. This is most
noticeable in the lower incisors possibly as a result of a change in interincisal angle
under the influence of soft tissue maturation and differential growth of the mandible
and maxilla with a tendency to prognathism and forward mandibular rotation. The
other factors often discussed in relation to late lower incisor crowding is mesial drift
of buccal teeth and the eruption of third molars. Many factors thought to be related to
late lower incisor crowding may include:
 Mandibular growth rotations which cause trapping of lower incisors behind upper
incisor and lead to lower crowding
 Anterior component of occlusal force that force the lower teeth to move mesially and
become crowded anteriorly.
 Degenerative periodontal changes that allow teeth to drift under light pressures;
 Change in diet and lack of interproximal wear as shown by Begg study on aboriginals
(Begg, 1954).
 Lower lip maturation which exert extra pressure on the labial surface of lower incisor
leading to crowding (Richardson, 1997).
 Mandibular third molars (Richardson and Orth, 1989), however a RCT by Harridan et
in 1998 (Harradine et al., 1998) showed that there is no correlation between impacted
third molars and lower incisor crowding but according to National Institute for
Clinical Excellence (NICE) guidelines, prophylactic orthodontic removal of wisdom
tooth is contraindicated.

Post-eruptive movement
Teeth continue to move in three planes of space after their full eruption at an
approximate rate of 0.4mm per annum. There is many reasons for post eruptive
movement including zompensation for occlusal and proximal wear as well as
accommodation for growth. The latter occurs to accommodate the final growth of the
jaws and usually complete by the late teens. Observing the effects of an ankylosed
tooth best sees the amount of growth occurs after eruption.

Assessment of Dental Age
The eruption times and sequences of the permanent dentition are influenced by
hereditary, environment, early tooth loss, infection, socio-economic and geographic
condition.
Moorrees & Kent (1978)233
Tooth emergence curves or “step-function” are constructed for the deciduous and
permanent dentitions. (Age in years vs. no. of teeth erupted) Validity of this method
is shown to be convenient and simple method.234,235 This method can only be
applied at ages when emergence can be expected. It is more valid in populations with
low incidence of such disturbing factors as caries. It does not depend on knowledge
of the exact emergence ages of specific teeth.
Moorrees & Fanning (1963)236
For each tooth the degree of calcification is determined according to arbitrarily
selected stages from OPG and compared to normal tables. Horizontal bars show the
chronology of tooth formation for each stage +/-1,2 SD’s. Dental development then
related to chronological age.
Three methods for estimation of chronological age based on tooth formation on
radiographs investigated by Hagg & Matsson (1985).237 The accuracy was at least
+/- 12 months for all methods in young age groups and +/-20 months in older
groups.238-240 Hence poor correlation, all methods contain subjective elements.
Dental maturation or dental Developmental age
It is an indicator of the stage of development of teeth and may reflect the
physiological growth of the person.

Application of dental maturation
1. Diagnosis and treatment planning
2. Forensic dentistry
3. Immigration purposes: it is proving valuable when birth data is lacking or doubted in
the management of immigration to help determine physiological age
There are two main methods to assess Dental maturation
1. Gingival emergence methods: This method may be influenced by local factors
(Ogodescu et al., 2011, Demirjian et al., 1973):
 Ankylosis,
 Early or delayed extraction of the deciduous tooth, impaction
 Crowding of the permanent teeth
 Genetically determined
1. Radiographic methods: In contrast to emerging method, the formation rate of the
permanent teeth is not affected by premature loss of the deciduous teeth. This can be
achieved by using panoramic radiographs or full mouth periapical radiography.
Example:
 Demirjian method (Demirjian et al., 1973) 8 stage technique, 7 stage technique and 4
stage technique (French-Canadian origin. 2500 males and 2500 female). It is better to
use 4 teeth method because chronologically lower incisor is almost the same as for the
first molar, and is often missing the central incisor. Also, for practical reasons, it is
often simpler to take a radiograph of fewer than seven teeth. However 4 teeth system
has limitation of inability to use in very young and very old children in the
standardizing sample.
 Nolla technique (Nolla, 1952)
 Haavikko technique (Haavikko, 1970)

Demirjian method
It involve the following steps:
A. The left mandibular teeth should be chosen for their minimum variability.
B. Either OPG or Periapical is used and the stage of each tooth is determined. There are
8 stages:
 Stage A: In both uniradicular and multiradicular teeth, a beginning of calcification is
seen at the superior level of the crypt in the form of an inverted cone or cones. No
fusion of these calcification points is observed.
 Stage B: Fusion of calcified points forms one or several cusps which unite to give a
regularly outlined occlusal surface.
 Stage C: Enamel formation is complete at the occlusal surface, dentine deposition has
started and the pulp chamber has a curved shape at the occlusal border.
 Stage D: Crown formation is complete, extending down to the cemento-enamel

junction. Beginning of root formation is seen in the form of a spicule.
 Stage E: The walls of the pulp chamber form straight lines. The root length is less
than the crown height. In molars the formation of the radicular bifurcation is seen like
a calcified point or a semi-lunar shape.
 Stage F: The walls of the pulp chamber form an isosceles triangle. The apex ends in a
funnel shape. The root length is equal to or greater than the crown height.
 Stage G: The walls of the root canal are parallel and the apical end is still partially
open.
 Stage H: The apical end of the root is completely closed and the periodontal
membrane has a uniform width around the tooth apex.
C. The stage of each tooth is converted to a numerical score and the sum is called
maturation score, two table are available for both genders.
D. The maturation numerical score is traced on the line chart using the 50th centile curve
as a guide in order to determine the patient dental age. There is curve for males and
curve for females.

E. To assess wheather the patient dental age is consistent with peers, resultant dental age
from previous step is traced against patient chronological age (Chronological age for
each patient was calculated by subtracting the date of birth from the date when the
radiograph was taken.). If the points intersected in the 3rd or 97th centile curve, this
mean the person has delayed or advanced dental development in comparison to
his/her peers respectively.

Example: Let us look at this OPG and repeat step A-E
Step A: Scoring
Tooth Stage
M2 12
M1 11.2
PM1 7.3
PM1 12.6
C 11.1
I2 12.5
I1 9
Step B: By looking at the males table, it was found that the maturation score is equal
to 75.7, Chronological age 7.9 years
Step C: According to the line graph for the boy, the patient dental age is 8.2 years and
his is following the 50th centile curve.

Chronology of development of the primary dentition (Foster and Hamilton, 1969b)
Teeth Crown Complete
(months)
Calcification (weeks
IU)
Eruption
(months)
A 1.5-3 13-15 6-9
B 1.5-3 13-15 6-9
D 6 14-17 12-15
C 9 15-18 18-20
E 10-11 16-23 21-35
Root development complete 1-1.5 years after tooth eruption

Chronology of development of the permanent teeth (Foster and Hamilton, 1969b)
Teeth Calcification begins
(months)
Crown Complete
(year)
Eruption
(year)
First molars Birth 2.3-3 6
Mandibular Central Incisors 3-4 4-5
6-7
Mandibular Lateral Incisors 3-4 4-5 7-8
Mandibular Canine 4-5 6-7 9-10
Mandibular First premolar 21-26 5-6 11-12
Mandibular Second Premolar 27-30 15-7 12-13
Second Molars 30-36 7-8 12-13
Third Molars 7-10 year 12-16 16-21
Root development complete 3 years after eruption

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