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CHRONOLOGY OF TOOTH DEVELOPMENT

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DENTAL MORPHOLOGICAL TERMS

Before starting a new topic in dental anatomy, we will talk about the process of "dental age estimation" by using "Gustafson & Koch Diagram", which is a nice diagram that represents the development of different stages related to each tooth. And it can be used as another reference for age estimation.

Each tooth in this diagram is represented by a line, for example, the line with sign is for tooth {37} in FDI notation system, and you can see that for each line there are 4 triangles:

The first triangle is for the 1st evidence of calcification

The 2nd triangle is for the crown completion.

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The Orange area

The Yellow area

The Blue area

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The 3rd triangle is for emergence.

The last triangle is for root completion.

The lower part of each triangle represents the lower limit of the age, the upper part is the higher limit, and the apex represents the average age. That means that there are differences in time between people in developing the first evidence of calcification, for example, for the same tooth.

If you take the crown completion triangle related to tooth 6 (the maxillary first molar) and follow the line, you will find that it will be completed at the age of 3 years. However, some people may have their crown completed at the age of 2 years or at the age of 4, so we have a wide range, but the average of this range is 3 years, and so on.

The blue area represents the months in-utero "Intra-uterine" (before birth), the yellow area represents the months after birth up to 1 year , then the orange area represents the years from 2 up to 16 years.

So we use:

Months ------------- before birth.

Months ------------- from birth to 12 months later (1 year)

Years --------------- from 2 – 16 years.

Anyway in our practical lab we will not use this diagram, instead we will use the tables, but if you once see it, you have to be able to use it.

Estimation vs. determination:

"Actually we don’t determine age, we estimate it"

If you have an X-ray you will be able to tell the age specifically and exactly, but if you don’t, then you will come up with a wide range.

If you want to estimate the age of a child in the mix dentition stage (deciduous and permanent dentition) then you can do it precisely, but if you want to estimate the age of a person who is over 25 based on his teeth, in this case it will not be that much easy.

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So we rely on other factors such as The tooth wear ( السن ذوبان If the . ( معدلperson is old this means that he has been using his teeth for a long period of time; that's why we expect to see flat surfaces which we call (tooth wear) .

Sometimes we depend on the development of periodontal diseases ( التهابباألسنان المحيطة for identifying age related probl The Means of ( األنسجة

investigation the age are:

1. Clinical examination

2. Models e.g. cast.

3. X-rays (OPG)

Why do we estimate the dental age????

We can use the estimated dental age in Forensic investigations: for example, if there is an unknown dead body for a child, the estimated dental age can help in identifying him, and to know the body age.

*** Previously in the middle ages they relied on the teeth data to estimate the age of a person, whether to accept him as a witness in the court or not ( if he is over 18 or not ) that means that he is wise, and has wisdom, from here the word "wisdom molar" came , so people without 3 rd molars are less wise !!!!

Steps for age estimation:

1- Locate the Medline and count the teeth.

2- Identify the whole teeth before age estimation and identify deciduous and permanent teeth.

3- Identify any abnormality: any abnormality has to be excluded.

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The age estimation will be much accurate for individuals in the mix dentition stage than that for adults

How can we predict abnormalities??

** For example, if you found that all the 2nd molars have erupted in all quadrants except in one, because it has melted, this is an abnormality >> that doesn’t mean that the tooth hasn’t erupted yet, but it means that it has failed to erupt, so actually this tooth should be cancelled.

In this case, Look at the contra-lateral tooth (the tooth on the other side) unless the abnormality is symmetrical (has occurred on both sides).

4- Choose teeth close to a “stage” whose age can be known from the chart: a good student will pick up a tooth that is near one of the stages, so look carefully if you find a tooth that is in the crown completion stage "take it". Don't take a tooth that is in the process of root development because in this way you will take time and in the exam we don’t have time!!! For root completion take teeth that are about to have a completed root, not teeth with a completed root, because that means that you will end up with "older than" and that will widen the range! < اختيار في ذكي كون < السن

***Take as many clues as possible. Try to take more than 1 tooth, don’t just rely on (the last tooth that has erupted, and the next tooth to erupt) rule. You may have a small interval, but sometimes you will face problems in the age estimation because of the abnormalities in the teeth.

EXAMPLES:

1- Find the age of this child??!!

There is a crown completion in tooth 7, which takes place at the age of (7-8) years.

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The root is complete for tooth 6 which takes place at the age of (9-9.5)

The maxillary lateral incisor is missing, that’s why you have to identify the problem and exclude it.

And the mandiblular lateral incisor has erupted which takes place at the age of 7.5.

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Here the last tooth that has erupted is (7) which is the second molar which erupts at the age of 12 years, but at the same time (5) has not erupted yet, but we know that it erupts first!! So we have a problem here.

In this case the age is over 12 years because of the emergence of 7, and under 12 because of the existence of a deciduous tooth, so over 12, under 12, so if you take 12 that will be good for this case.

3- What the age of this child???

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So the age will be between (7.5-9)

So the age is 12

Apparently he is not a child; he is an old man that has lost all his teeth, because there are no teeth in his jaws. So how exactly can we tell the age??

When we have a case of an adult where all his teeth has erupted in addition to the 3rd molar, here we just say that he is over 25, but we try to depend on other factors, such as peridentitous?? That takes place at the age of 40, so we say it is from 25-40 years.

By this we finished age estimation, and now we will move to a new topic which is:

DENTAL MORPHOLOGICAL TERMS (dental terminology)

Morphology: the science of shape (form) that has 2 parts: the shape and the size.

Anatomy: the science that describes the structure of enamel, dentin and the relationship between teeth, not just the form. So "dental anatomy" has more details than "dental morphology" .that's why the course name is (Dental Anatomy) not (Dental Morphology).

Human dentition is diphyodont -as we know- we have the primary dentition and the secondary dentition

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1- Primary (deciduous/ predecessor) dentition

Formula: I 2/2 C 1/1 M 2/2

Eruption: 6 months - 28±4 months

Shedding: 6 to12 years

2- Secondary (permanent/successor) dentition

Formula: I 2/2 C 1/1 P 2/2 M 3/3

Eruption: 6 to (18-25) years

This table represents the dimensions of each of the deciduous teeth, for example, if you take (the central incisor) the crown height is 6 mm, the root length is 10 mm, the mesiodistal width is 6.5 and the buccolingual width is 5 mm.

>>You can notice the differences between the maxillary teeth and the mandibular one<<

You have to remember that each tooth consists of a crown and a root, and each crown has 5 surfaces:

1- The surface that faces the outside toward the lips and cheeks.( Facial surface )

• Facial can be divided into: - labial if you talk about anterior teeth.

-Buccal if you talk about posterior teeth.

2- The surface that faces the inside toward the tongue in the lower jaw is the lingual surface, and towards the palates in the upper jaw is the palatal surface. (and sometimes we also use lingual for maxillary teeth )

3- The surface that faces the midline is the mesial surface.

4- The surface that faces away from the midline is the distal surface.

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You don’t have to remember these numbers; however, you need to remember the teeth that we will carve.

5- The surface that is toward the upside is called the occlusal surface.

In all teeth the mesial surface of one tooth meet with the distal surface of the adjacent tooth except in the central incisors (the mesial surface of one incisor meets with the mesial surface of the other one).

**** the 3rd molars have one mesial surface that is in contact with the distal surface of the 2nd molars ,but their distal surfaces are not in contact with any other tooth.

The stages of human dentition:

• Edentulous stage( 0 - 6 months ): we don’t have any teeth in the mouth during this stage

- it is from birth until 6 months (which represents the emergence of the mandibular central incisor)

• Eruption of primary dentition (6 months-2.5 years): during this stage we have the emergence of the primary dentition.

• Functioning primary dentition (2.5 – 6 years): This is after the emergence of the last primary tooth, when the child starts using his primary teeth.

• Mixed dentition (6 – 12 years): where we have the first permanent tooth, and it ends with the loss of the last deciduous tooth (in Jordanian population we have 3 deciduous teeth that will be lost at the same time which are the maxillary canine, the maxillary 2nd premolar, and the mandibular 2nd premolar) which takes place at the age of 12.

**Remember that we have 2 sub stages: 1- the early mix dentition

2- The late mix dentition.

During the early stage the eruption of the first molars and the incisors will take place, and during the late stage the premolars and the canines will erupt, too.

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Edentulous = no teeth

• Permanent dentition (over 12 years) where the whole permanent teeth have erupted with the addition of the second molars.

• Full permanent dentition (18-25 years) which is after the eruption of the 3rd molars (if present), some people say that this stage is established with the eruption of the 2nd molars not the 3rd, because many people have missing 3rd molars.

This is the deciduous arch.

And this is the permanent arch.

Why we call it arch? Obviously because it looks like an arch

***What is the difference between arch and jaw??

The jaw includes the teeth, the bones that support these teeth and the mucosa or the gingivae that covers the bone. But the arch expresses only the teeth (the arrangement of these teeth in the form of arch, so they are called dental arch) < maxillary arch and mandibular arch >.

Regarding the incisors, the occlusal surface is constricted (very small) so for anterior teeth ( the incisors and the canines ) instead of having wide

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occlusal surface we have very constricted one, actually it is not a surface it is a ridge, that’s why it's called incisor edge/ridge < المفك . < مثل

Teeth also can be classified into classes:

There are 4 different classes in permanent teeth: the incisors, canine, premolars, and molars.

Where the classes of the deciduous are 3: incisors, canine, and molars (we don’t have premolars)

-In the class of incisor there are 2 teeth in one quadrant.

-In the class of premolars there are 2 teeth.

-In the class of molars there are 3 teeth.

-In the class of canine we only have 1 tooth

** Remember that this is not the maximum number of teeth in each class, we as human beings actually have the maximum number of teeth in the canine class and in the molar class, but we don’t have the maximum number of the incisor class and in the premolars, because the maximum number of incisors in mammals is 3, and the maximum number of premolar is 4.

*** The function of the incisor is to incise > to cut (قواطع (

Identification traits

We have to identify teeth among each other and differentiate between them.

* Set traits : are the characteristics that distinguish deciduous teeth from permanent teeth, e.g. size is one of these traits, tooth color also, because deciduous teeth are whiter in color than permanent.

Arch traits : are the characteristics that distinguish maxillary teeth from mandibular teeth of the same class. For example, if you take the central maxillary incisor and the central mandibular incisor, the maxillary incisor is wider.

Class traits : are characteristics that distinguish different classes of teeth. For example, the tooth with one cusp is a canine that differs from

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other classes of teeth. If you see a tooth with an incisal edge this is a class trait that distinguishes this class from others.

Type traits: when you have more than one type of tooth in each class, e.g. we have 2 incisors and 2 premolar, and 3 molars. for example, if you want to distinguish maxillary central incisor from maxillary lateral incisor, both of them relate to the class of incisor, both of them are located in the maxilla, both of them are permanent, but the width for example can be used as (a type trait) that enables you to distinguish between two teeth belonging to the same class, arch and set. Similarly, characteristics used to distinguish between the 2 premolars are called type traits.

But if you want to distinguish between the maxillary first molar and the mandibular first molar, in this way you don’t use type trait, you will use arch trait because they are in different jaws.

Terms related to anterior teeth:

**What is the meaning of anterior teeth & posterior teeth??

-Anterior teeth: They are the teeth that are located in the front of the mouth, where the limits of the front of the mouth are the canines, so -canines and incisors are the anterior teeth.

-Posterior teeth: are the teeth that are located at the back of the mouth, and that includes the premolars and molars.

- Line angle: is any angle between 2 surfaces.

The angle between the buccal surface and the occlusal surface is not in the form of a point but it is a line, that’s why we call it (line angle). So we have a (Buccal-occlusal line angle), (mesio-buccal line angle), (mesio-lingual line angle).

*Note: we don’t have a bucco-lingual line angle, because the buccal surface and the lingual surface are opposing each other and don’t meet.

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Cheek teeth = the posterior teeth (premolars and molars) because these teeth face the cheek.

A student asked if there is a bucco-lingual line "in the incisors"??

The Dr answered: NO, we don’t have bucco-lingual line even in the incisors because all teeth have 5 surfaces including the anterior teeth.

-point angle: the meeting of 3 surfaces together, E.g. If you take the buccal, mesial and occlusal surfaces, all of them meet at one point which is called a "mesio-bucco-occlusal" point angle.

-Incisal edge: it is the edge between the labial and the incisal surface, which is only found in the incisors, and it is one of the line angles.

-Cusps: is an elevation on the occlusal surface of the tooth, like a hill.

They are found in molars, premolars and canine.

-Canine has one pointed cusp.

-Premolars have 2 cusps: one elevation lingually and one elevation buccully.

-Molars have 3 or more cusps: usually they are flattened not pointed, but the cusp of premolar is pointed as well as the cusp of canine.

However, there are no cusps on the incisor, instead we have Cingulum.

If you look lingually from the inside at the incisor you will find an elevation near the neck of the tooth which is called Cingulum.

-Fossa: is a depression that can be seen from the inside of the tooth. (The lingual fossa)

Fossa is the opposite of cusp.

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-Ridge and marginal ridge: when the incisors erupt, their incisal surface will be pointed (incisal ridge). The labial surface ends and meet with the lingual surface without an edge, but with time tooth wear takes place, which will produce a flat part which is the incisal edge.

So all of us had incisal ridges only in the few months after the eruption of the incisors, and then we will all have incisal edges.

Marginal ridge: is any ridge that is located on the margin of the tooth .for example, the lingual surface of any tooth has a ridge that is called (marginal ridge).

The lingual fossa inside is surrounded by 4 things: mesial marginal ridge, distal marginal ridge, a Cingulum and the incisal part of the tooth.

In posterior teeth marginal ridges are different and they are perpendicular to the long axis of the tooth.

-Cervical line: is a line that binds the end of the crown and the beginning of the root.

The crown is covered with enamel, and the root is covered with cementum, the junction between the crown and the root is called the cervical line.

-Lobes: are segments that fuse with each other to form the crown of the tooth.

Each tooth has 3 lobes; the mesial, the middle, and the distal lobes. When they fuse together they form the crown.

-When the teeth have erupted they were like < fruit knife > each one is called Mamelon, they are mesial, middle and distal Mamelon. But with time because of using these teeth the Mamelon will disappear.

-Lingual pit: is a pit located at a very deep point of the lingual fossa.

_____________________________________________________The End

Done by: Enas Y. Salameh

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