7+8 - · pdf filethe tooth has emerged but is still not functioning because its still out of...

Yasmeen Al-Khatib Pedo Sheet No.7+8 29/03/2015

1

7+8

29/03/201

5 Dr. Suha Abu ghazaleh

Yasmeen Al-Khatib


1

Eruption and Arch Development

Lecture’s Outline (lec. 7):

Life cycle of teeth

Pre-eruptive period

Period of eruption of primary dentition

Static period of primary dentition

Life cycle of teeth will not be discussed in the lecture. The doctor gave us a handout

regarding this topic that is required from us for the final and it talks about the

histology of teeth as it starts development.

Pre-eruptive period:

Characteristic of the pre-eruptive period:

Extends from the moment of birth up to 6 months of age or until the first tooth erupts.

In general all infants look alike and bony face and skull show little differentiation

from child to child. Generally, the face appears broad and flat due to lack of vertical growth.

Bones of the cranium are separated by soft membrane filled gaps or called Fontanells that

close at age of 2 years. The moment the baby is born, the head occupies ¼ of the bone of

the whole body and changes to become 1/7 in adults. Neoborns have tiny mouth and no

chin. The mandible is retrognathic and underdeveloped. Like adults, the maxillary anterior

gum pad or the intercanine distance is typically wider than the lower anterior gum pad.

They usually have an overjet of 5mm and an overbite of 0.5mm in most children. They do

show marked increased in the palatal width and decrease in the overjet in the first 6

months. Newborns show hypertrophic labial frenum that has nothing to do with suckling as

well as hypertrophic retroincisal papilla (incisive papilla). Newborns have large tongue due

to the retrognathic mandible. The palate in the beginning is more straight and then gets

concave during development.

All the previous features are normal and you have to assure the parents who come

complaining of any.


Common findings of the oral mucosa of newborns:

1) Epstein Pearls:

They are small white/greyish lesions. They occur in about 80%

of neonates. They are formed along the midpalatine raphe.

Histological sections show remenants of epithelial tissues

crowded along the palatine raphe.

They disappear after few weeks of life. Parents should not be

worried about them as they eventually disappear.

2) Bohn Nodules:

They are formed around the buccal and lingual aspects of the

dental ridge and on the palate but away from the midpalatine

raphe.

Histologically, they show mucus gland tissues. They also

disappear spontaneously but take a little bit more time than

Epstein Pearls within the early months.

3) Dental Lamina Cyst:

Their location is on the crest of the maxillay and mandibular dental ridges that is

exactly where teeth usually erupt from. Parents are more aware of this feature as

they think that this is a tooth. They are remenants of the dental lamina under the

microscope. And they also disappear through the

first months of life. No treatment is required.

Differential Diagnosis:

- Natal Teeth: some newborns are born with teeth

but you can differentiate it with the cyst that the

natal teeth is hard and resembles a tooth in

contrast to the cyst that is soft in texture.

Infantile swallowing:

Suckling is a reflex essential for the survival of the newborn.

The infant places the tongue beneath the nipples in contact with the lower lip. Jaws

are usually apart. The lips are pressing together thus getting a strong lip activity. Persistant

infantile swallowing or tongue thrust can give rise to an anterior open bite.

At 6 months, the baby starts eating solid food. We will get a gradual transition

towards mature adult swallowing pattern and persists up to 5 years of age. The pattern is


that you get teeth together in contact. The tongue presses against the palate. And the lips

are relaxed.

Feeding of infants:

We always recommend natural breastfeeding. Human milk is the preferred food for

infants. For us as dentists, breastfeeding exerts beneficial orthopedic forces on the jaws

during development. Natural breastfeeding promotes better jaw growth.

There is a significant difference in the growth of the jaws and in muscle activity

between breast-fed and bottle-fed infants. Also they found that there were less pacifier

.use in breast-fed infants (اللهاية)

We as dentists should inform the mother about the advantages of breastfeeding. In

general we recommend breastfeeding up to 6 months of age.WHO recommends

breastfeeding up to 2 years of age.

Period of eruption of primary dentition:

It starts at 6 months in most of the children and is established by 30-36 months. We

expect most children by the age of 3 years to have all primary dentition erupted.

Maximum jaw growth occurs during this period.

Calcification:

It starts between 4-6 months of intrauterine life for primary teeth. Like permanent

teeth, primary teeth starts calcification from the cusp tips and incisal edges and continuous

cervically. It is a very sensitive process that takes place over a very long period of time.

Any severe systemic event during development of

teeth will result in some dental anomalies distributed on

teeth depending on the level of development. Thus they are

called Chronological Enamel Defects. Different teeth will

show different defects on the level of the crown depending

on the stage of crown formation.

Eruption:

The term eruption in general means the movement of teeth within and through the

bone of the jaw and the overlying mucosa to appear in the oral cavity and contact the

opposing teeth. While Emergence is the term we usually use. It means the first sign of

appearance of a tooth in the oral cavity.


3 phases of eruption:

1) Pre-eruptive phase:

The period in which the root begins formation and begins to move towards the

surface of the oral cavity from its bony part. Movement within bone.

2) Eruptive phase (Pre-function):

The period of gingival emergence until contact is achieved with the opposing

tooth. The tooth has emerged but is still not functioning because its still out of

occlusion.

3) Functional eruptive phase:

After the tooth meets its antagonist. It’s a dynamic process and continuous

throughout the life of the tooth.

What causes eruption?

We have many theories explaining eruption but still none of them is said to be the

actual cause. Eruption is a multifactorial process. Theories were hard to do on humans so

they are mostly animal studies.

First theory: Rooth Formation: Space for the growing root is accommodated by occlusal

movement of the tooth crown.

Second theory: Hydrostatic Pressure within the periapical tissues pushing the tooth

occlusally.

Third theory: Bony Remodeling that is pushing the tooth occlusally.

Fourth theory: Pulling of the tooth occlusally by the cells and fibers of the periodontal

ligament.

No hypothesis that fully explains tooth eruption. Its multifactorial.

Deciduous teeth:

- They are 20 in number, 10 in each jaw.

- There are no premolars in the deciduous dentition.

- First primary molars are replaced by permanent first premolars.

- Permanent molars erupt distal to the primary second molars. Parents usually

come with fear that there is a tooth erupting without another tooth being lost. So

we have to assure them by telling them that this is a permanent tooth that is

erupting in its normal place. This might be a motivation for the parents to

enhance oral hygiene methods at the moment they know that this is permanent

tooth.


- Beginning from the midline, teeth are central, lateral, canine, first molar and

second molar.

Tooth numbering:

We have different systems:

1) The palmer notation: children’s 20 teeth are labelled in letters from A to E in each quadrant. This notation is

the one we still use.

1) Universal numbering system: mostly used in USA. Each tooth has its own number in permanent teeth or letter

in primary teeth.

1) FDI system (two-digit notation):

permanent teeth quadrants are designated as 1,2,3 and 4. Primary

teeth quadrants are numbered 5,6,7 and 8. Then each tooth is given its

own number plus the quadrant number.

Chronology (timing):

The first tooth to erupt is usually at 6

months and is usually the lower centeral incisor.

6 months is not a must. Many children become

older than 1 year and they still don’t have their

lower central incisors. We should always be

conservative. Always assure the parents that

there is variation and they are normal. We should

follow-up.

All eruption schedules are estimates.


Because we use the estimated numbers for another society, we always find variations.

Recently there is an article puplished talking about the eruption schedule in Jordanian

population. No two individuals are alike. All estimates depend on race, gender, ethnicity,

environment and heredity.

In general, we need a reference to follow and that is the 6 months.

Sequence of eruption: A,B,D,C,E. Usually

the mandible preceeding the maxilla.

Rhythm of eryption:

We usually get a symmetrical groups of 4 teeth erupting every 6 months in both jaw,

simultaneously, and in pairs.

The six/four rule for primary tooth emergence:

- At 6 months: 4 teeth erupt (lower and upper As)

- At 12 months: 8 teeth erupt (lower and upper As and Bs)

- At 18 months: 12 teeth erupt (lower and upper As, Bs and Ds)

- At 24 months: 16 teeth erupt (lower and upper As, Bs, Ds and Cs)

- At 30-36 months: 20 teeth erupt (that is the full primary dentition)

Static period of primaty dentition:

All primary teeth are erupted and no permanent teeth yet. It is the period of

stability of primary teeth from 3-6 years of age. The child has the 20 primary teeth in

functional position and occlusion is well established.

Occlusal features of primary dentition:

- Usually in all children we have generalized spacing.

- Incisor teeth tend to be spaced.

- We also have the primate space that exist between upper B&C and lower C&D.

- Upper incisors are usually upright and the incisal relation is more towards edge-

to-edge relationship.

- Long axis of primary teeth is parallel.

- Absence of curve of spee.

(in months) Maxilla Mandible Central Incisor (A) 6-10 5-8

Laterial Incisor (B) 8-12 7-10

Canine (C) 16-20 16-20 First Molar (D) 11-18 11-18

Second Molar (E) 20-30 20-30


- In general, primary dentition tend to be well-aligned if there were no caries.

When their permanent teeth starts erupting, they start showling mal occlusion

and some darkness in color. Usually parents don’t like that and complain of this as

the older primary dentition was perfect in their opinion. We should assure parents

as it is a normal feature.

Classification of occlusion of primary second molars:

By looking at the distal aspect of the primary second molar, we either have flush

terminal, mesial step (lower mesial to the upper) or distal step (lower distal to the upper).

We should observe this classification before the 6s erupt because once the 6s have erupted

we forget this classification and switch into angel’s classification.

Inter-arch relation of primary teeth:

How do we get occlusion? It is mostly like the permanent teeth. Each tooth occludes

with two opposing teeth, except for the lower central incisors (occludes only with the upper

centrals) and the upper second molars (occludes only with the lower second molar).

Canines are the key of occlusion of primary dentition and we need to look at the long

axis of the canine. It should be placed in the midline between the lower D and C as a class I

relation. Natural wearing of the canine is an important physiological process that facilitates

movement of the mandible. If that did NOT happen, children raised on soft food usually

come with a crossbite because there were no wearing of the canine. This case is very

simple. We may have to carry out gradual selective grinding of the primary canines

especially in the presence of a unilateral crossbite. Gradual grinding is important to avoid

teeth sensititvity.

Period of mixed dentition

This is the start of the second lecture (lec. 8)

Lecture’s outline:

Causes of shedding of primary teeth.

Resorption pattern of anterior and posterior primary teeth.

Chronology of eruption of permanent teeth.

Eruption of permanent teeth.

Period of mixed dentition starts from 6 years up to 12 years of age.


Shedding of primary teeth:

- It is the result of the progressive resorption of the roots of teeth and their

supporting tissues.

- It’s a physiological process.

- It is accomplished by multinuclear odontoclasts. Odontoclasts are exactly like

osteoclasts in function but are specific to dentition.

- We have periods of rest and repair.

- At the end, resorption predominates and the tooth eventually exfoliates. They

either fall by themselves or patients come to us and we extract them.

What are the causes of shedding of primary teeth?

There is no known cause but there are proposed theories.

First Theory: Pressure from the erupting successor tooth initiates resorption process.

Eventhough, primary teeth with no permanent successor beneath it end up with resorption

and shedding at last. This is why this theory is not that much supported because its not the

only cause of shedding of primary teeth.

When the successor is missing, shedding of the primary tooth is delayed but not

stopped. But when there is an underlying permanent successor, shedding is accelerated.

Second Theory: Forces of mastication that are greater than periodontal ligament of a

deciduous teeth can withstand. We get trauma to the PDL and that initiates resorption.

Resorption pattern:

Anterior teeth:

Permanent teeth undergo complex movement before they reach the position

from which they will erupt (that is the pre-eruptive movement). Anterior teeth

usually start erupting lingual to the primary teeth and then when the primary teeth

sheds, they move more apically and occupy their own bony space.

When you take the tooth out and look into the socket, you will find the

permanent successor in there. As well as the primary teeth will show lingual

resorption when taken out due to the pattern of resorption of permanent teeth.

Premolars:

The same thing applies here. Resorption starts lingual to the primary molars

and then they move more apically in between the flaring roots of the primary molars.

The change in position provides the premolar with adequate space to continue their

development. This is the reason behind having divergent roots of primary molars.


Chronology of Eruption of permanent teeth:

As we all know, the first tooth that erupts in permanent dentition is the first

permanent molar and sometimes can be the centrals. Usually the lower teeth erupt

before the upper teeth.

Sequence of eruption:

In the mandible:

6,1 – 2 – 3 – 4 – 5 – 7 – 8

In the maxilla:

6,1 – 2 – 4 – 5 – 3 – 7 – 8

Eruption timing in girls generally preceed

boys by an average of 5 months.

Premature loss of primary molars:

Very early loss (at age of 5) of primary molars will lead to delayed eruption of the

permanent premolars. If extraction was after the age of 5, the delayed eruption will

decrease in magnitude. If extraction occurred at the age of 8,9,10 years, premolars

eruption is accelerated.

Sequence of eruption is very important. Always count the number of teeth when

examining any patient either child or adult.

Sequence of eruption and variations:

- There is no significant variation in erupting of the 6s before the 1s or the opposite.

- It is desirable that the mandibular canine erupts before the lower first and second

premolars. This aids in maintaining adequate arch length and prevents lingual

tipping of the incisors.

- If the mandibular second molars (7s) erupt before the lower second premolars

(5s), this will result in decreased arch length. This is due to mesial migration and

tipping of the 6s and encroachment of space needed for the second premolars.

- Untimely loss of the primary molars in the maxillary arch may allow the first

permanent molars to drift and tip mesially resulting in the permanent canine to

be blocked out of arch.

- As we all know, the most teeth to be blocked and remain impacted are the

canines in the upper jaw and the second premolars in the lower jaw.

(in years) Maxilla Mandible 1 7-8 6-7

2 8-9 7-8

3 11-12 9-10 4 10-11 10-12

5 10-12 11-12

6 6-7 6-7

7 12-13 11-13

8 17-21 17-21


Rhythm of eruption:

We have three stages:

1) Early Mixed Dentition: we have incisors and the first molars erupted.

2) Late Mixed Dentition: we have the canines, premolars and second molars erupted.

Teeth erupt symmetrically in both jaws simultaneously and in pairs.

3) Third Molar Eruption: is a late stage that is seen later on.

We have rules to help us in memorizing:

Rule of 4 for permanent tooth development:

- At birth: the 4 first molars starts calcification (sometimes the centrals are

involved).

- At 4 years: all crowns have initiated calcification.

- At 8 years: all crowns are complete.

- At 12 years: all crowns have emerged.

- At 16 years: all roots are complete (that is 3 years after eruption).

Rule of 3:

- Crowns are completed at least 3 years before eruption.

- Roots are completed 3 years after eruption.

- Teeth erupt when ¾ root development has completed.

Hard tissue formation:

When is enamel completed? As we said, that’s 3 years before eruption.

6s 2 ½ -3 years

1s, 2s and 4s 4-6 years 3s, 5s and 7s 6-8 years

8s 12-16 years

6s At birth of slightly

before

Upper 1s and 3s Lower 1s, 2s and 3s

At 3-6 months

Upper 2s At 10-12 months Upper and lower

premolars and second molars

At 1 ½ -2 years

Upper and lower third molars

At 7-10 years


Eruption of permanent teeth:

1) Lingual eruption of mandibular permanent incisors:

- It’s a very common phenomenon.

- It’s a cause of concern to parents.

- It is seen in patients with obvious arch length

inadequate space and crowding. This is not a must

because even children with no crowding and have

spacing show lingual eruption of the permanent

incisors.

- Its not because of crowding.

- The cause behind this is what we said before is that incisors start shedding the

primary teeth lingually and then shift apically. In this case the bud did not move in

an apical direction and erupted lingually.

- When examining primary teeth, they may be very mobile and held only by soft

tissue or they may not undergo normal resorption and stay solid in place.

- Management is that we leave the primary teeth if they were mobile. If not, we

extract them.

- Position of the permanent incisor will improve over several months. It’s a self-

correcting case.

- We should not extract any other primary teeth than the primary centrals. Some

people think that the permanent teeth need more space and they extract the

primary centrals and laterals and that is wrong!

- The tongue plays and important role in influencing the permanent incisor into its

normal position with time.

- We should assure the parents, and follow up.

- If the condition is identified before the age of 7 ½ years, we do not interfere, we

only follow it up.

- If it was in an older child and when the primary tooth shows no resorption on

radiographs, we should extract the primary incisors.

- Labial migration of the permanent incisors usually occurs naturally with or

without the removal of the primary teeth.

- Removal of the tooth during the first dental visit may not be a great introduction

into dental surgery for a child who only came for check-up.

- Still some parent are alarmed when they see such condition.

- If that happened in the upper incisors, self-correction will not be achieved as

there is not tongue and is much harder to control than the lower incisors. We


usually follow up or exert pressure using orthodontic appliances to push them

anteriorly.

2) Ankylosed primary molars:

- They are also referred to as Submerged Teeth or Teeth Infraocclusion.

- The ankylosed tooth is in state of static retention.

- Adjacent teeth keep erupting but this tooth remains still in place as it is ankylosed

in bone.

- The most affected teeth are the mandibular

primary molars.

- It is of unknown cause.

- It is familial. Ankylosis was noticed in several

members of the same family.

- An absence of the permanent successor has

been implicated with ankylosis. There is a

strong relation between the congenital absence

of the permanent teeth and ankylosed primary teeth.

- As we said, normal resorption has periods of rest and repair. This condition occurs

in the rest stage. Unity of the bone and the root of the primary teeth appears.

- How do we diagnose it?

Clinically, we see infraocclution.

Upon tapping the tooth, you will hear a solid sound (that is bone) vs. normal

cushioned sound (that is the PDL)

Tooth is absolutely not mobile.

Radiographically, you will observe break of the continuity of the PDL.

- Management:

Keep the tooth under observation. Tooth may later on undergo root

resorption and shed by itself. We should always start conservative.

If the permanent successor is missing, establish occlusion with a stainless

steel crown or bounded restoration. We have to try our best to keep this

tooth as there is no permanent tooth beneath it. Brining it into occlusion

increases the functional forces on the PDL that will aid in removing the

ankylosis.

The last option is when the patient shows increased caries rate and loss in

arch length, we might end up having to surgically take the tooth out and its

not an easy procedure.


3) Eruption Sequestrum:

- Seen in children at the time of eruption of the first permanent molars.

- It is a hard tiny spicule of non-viable bone overlying the crown of an erupting

permanent molar just before or immediately after the

emergence of cusp tips through the oral mucosa.

- The sequestrum develop from either osteogenic or

odontogenic tissue.

- Its position is generally found overlying the central

fossa of the associated tooth and is embedded within

soft tissue.

- Some of these sequestrums sponateously resolve. If its

causing local irritation, it is easily removed. Its very

simple, we only give topical or infilteration anesthesia to avoid discomfort.

4) Ectopic eruption of the first permanent molars:

- First permanent molars may be positioned too far mesially causing resorption of

the distal root of the second primary molar.

- Mostly affects the upper 6s that show mesial path of

eruption. They end up being locked behind the Es causing

root resorption of the Es.

- We have two types:

Reversible: molar frees itself and goes back to its normal path of eruption with

the Es remaining in their position. Occurs by the age of 7 years. 2/3 are self-

correcting. No significant differences were found in those children.

Irreversible: molar remains unerupted and in contact with the cervical area of the

roots of the second primary molar. Only the distal part erupts. It is considered

irreversible by the age of 7-8 years.

- Features of the irreversible type are:

They showed significantly larger permanent first molars.

More pronounced mesial angle of eruption.

They have a tendency to have a shorter maxilla in relation to the cranial

base.

- What happens if it was ignored?

Premature loss of Es and a resulatant decrease in arch length.

Asymmetric shifting of the upper first molars into class II (only in one side).

Supra-eruption of the opposing lower molar causing distortion of the curve

of spee and potential occlusal interferences.

- Prevelance is low 3%.


- It is seen more frequently in boys more than in girls.

- It occurs in more than one quadrant most oftenly in the maxilla.

- There is a familial tendency with the prevelance of 20% in affected siblings vs the

overall 2-3% in general population.

- Frequent occurance in 25% of the cleft lip and palate due to the maxilla

positioning and nasal arch size.

- Management:

If it was detected early by the age of 5-6 years, we only observe and

monitor it.

If after the age of 7 years, it requires intervention.

When the opposing molar reaches the level of the lower occlusal plane,

intervention is indicated to stop it from over erupting.

- Approaches include: use of seperators or distalizing ortho appliances.

Seperators:

The first thing we start with is the orthodontic elastic seperators. We

gradually push the first molar distally. Every appointment we check the

elastic and replace it with a larger one to increase the forces applied for

distalization.

We can also use separating metal springs.

Brass ligature wires can also be used. We keep tightening it up every 3-5

days.

Distalizating orthodontic appliances: used in severe ectopic eruption.

5) Incisor Liability:

- It refers to when the permanent incisors are larger than the primary incisors.

What matters here is how are we going to have enough space to accommodate

the permanent incisors in a small space.

Inter-dental spacing of the primary incisors:

It is favorable for us but not to parents. Spacing in primary teeth provides

larger space for the larger permanenet ones. Thus, no crowing is observed

later on.

Primary teeth alignment Permanent teeth alignment

Crowding Almost will need extraction

No spacing Possibly needs extraction in the future Fair spacing Mild-to-moderate crowding

Good spacing No-to-mild crowding Excess spacing No crowding

- Fair and good spacing are mostly preferred to be seen.


Inter-canine arch growth:

It is a mechanism that helps in accommodating a larger space for the

permanent dentition. The mandibular inter-canine arch growth occurs mostly

during permanent incisor eruption and continues up to 9 years of age.

Labial positioning of the permanent incisor:

Permanent incisors erupts more labially angled.

Favorable size ratio between the primary and permanent incisors:

This is genetic.

Favorable type: we have larger primary teeth and small permanent ones.

Unfavorable type: we have smaller primary teeth and larger permanenet ones

and we end up with crowding.

6) Leeway space:

- Is the amount by which the combined size of the C,D and E exceeds the combined

mesiodistal width of the permanent 3,4 and 5.

- The average is 1.5 mm in the upper arch and 2.5 mm in the lower arch.

7) Late mesial shift:

- Refers to mandibular permanent molars moving mesially

and this is good if the primary molars are edge-to-edge .

- It allows permanent molars to move into class I occlusion.

The flush terminal pattern always leads to class I or class

II occlusion or stays end-to-end.

The mesial step leads to class I or class III occlusion.

The distal step always leads to a class II occlusion.

Wishing you all the best of luck ^_^

Yasmeen Al-Khatib :)

7+8 - · pdf filethe tooth has emerged but is still not functioning because its still out of...

Documents