Eruption of Teeth - Man’s Dental Formula

Dental formula is the conventional way of describing the number of each type of tooth in a man. It is the same dental formula used in other species. The type of the teeth is indicated by a letter, then followed by the number of teeth on one side of the upper jaw and then followed by the number of teeth on one side of the lower jaw. And because we consider in the formula only one side of the mouth, then the total number of teeth is the multiplied by 2.

Example in the Case of Man’s Dental Formula

Let’s look at an example in the case of man’s dental formula. We start by defining the four letters used in the formula.

I = Incisors teeth

C= Canines teeth

P = Premolars teeth

M = Molars teeth

For an adult man with 32 teeth, the formula is written as:

I - 2/2     C - 1/1    P - 2/2    M - 3/3

The total number of teeth on one side of the mouth is 16, and then the total number of teeth in the mouth equals 16 x 2 = 32

Now let’s now look at the picture above, which shows the teeth in the mouth of a man, together with the dental formula of a man which is:

I - 2/2   C - 1/1   P - 2/2   M - 3/3

You can see as follow:

1.  I – 2/2: represent (a) two teeth of central incisor and lateral incisor on one side of the upper jaw, and (b) two teeth of central incisor and lateral incisor on one side of the lower jaw

2.  C - 1/1: represent (a) one tooth of canine on one side of the upper jaw, and (b) one tooth of canine on one side of the lower jaw

3.  P - 2/2: represent (a) two teeth of first premolar and second premolar on one side of the upper jaw, and (b) two teeth of first premolar and second premolar on one side of the lower jaw

4.  M - 3/3 : represent (a) three teeth of first molar, second molar and third molar on one side of the upper jaw, and (b) three teeth of first molar, second molar and third molar on one side of the lower jaw

5. The total teeth in 1, 2, 3 and 4 above are 16 teeth. And because we have considered only one side of the mouth, then we have to multiply 16 by 2 to get 32 teeth for the whole mouth.

Thirty-Two Permanent Teeth in man

We have therefore seen that in an adult man, there are thirty-two permanent teeth, sixteen in the upper jaw and another sixteen in the lower jaw. The teeth are also arranged in symmetrical sets of eight teeth on each side.

Biting Part of Each Tooth is Called Crown

The biting part of each tooth is called crown. The crown is covered by enamel. Every tooth has a neck which is surrounded by the gum. Every tooth has one or more roots called fangs fitting into sockets in the jaw bone.

Chisel-Shaped Crowns

Incisors teeth have chisel-shaped crowns. The central incisor of the upper jaw is broader than any of the others. The central incisor of the upper jaw bites against the central and lateral incisors of the lower jaw. This is the same for every tooth in the upper jaw to bite against its corresponding tooth of the lower jaw and the tooth behind that, except for third molar.

Peg-Shaped Crown

Canine tooth has a crown which is peg-shaped and premolars and molars teeth have crowns which are flat. The upper premolars have each two roots while the lower premolars have each one root. The upper molars have each three roots while the lower molars have each two roots. As the upper teeth overlap the lower teeth externally, then by this the lower molars shows some rounding due to wearing away of the edge of the grinding surface of the crown on the outer side.

Wisdom Tooth

Of the three molars, the first molar is the largest, and the third molar (also known as wisdom tooth) is the smallest. The upper wisdom tooth is smaller than the lower upper wisdom tooth.

Milk Teeth or Temporary Dentition

In children, we have teeth called milk teeth or temporary dentition. In children there are only twenty teeth, ten in each jaw and five in each segment. They are

1. Two incisors

2. One canine

3. Two molars

Adult Molars Belong To The Milk Dentition

The two molars in children occupy the position which the permanent premolars later on take. The adult molars are thought to belong to the milk dentition. The adult molars cannot appear until the jaw has grown backward sufficiently to make room for them. The milk teeth or temporary teeth differ from the permanent teeth in:

1. milk teeth or temporary teeth have smaller size

2. Milk teeth or temporary teeth are whiter in colour

3. Milk teeth or temporary teeth have greater constriction of their necks

4. Milk teeth or temporary teeth have roots of their molars widely spaced

Children Teeth

In children, the lower central incisors come first between the sixth and ninth month after birth. Then, after two to four months, the central and lateral upper incisors come. They are then followed by the lower lateral incisors, then followed closely by the first milk molars. After another short rest comes the canines, the eruption of which is a slow process. By the end of the second year the first and second molars have appeared, and the milk dentition is complete.

Eruption of Permanent Teeth

The determining cause of eruption of the teeth is the growth of the roots and blood-pressure. When the milk teeth are shed, what is shed is a mere shell of the crown, all the root having been absorbed by the direct pressure of the succeeding tooth.

1. The first permanent tooth to come out is the first molar, and this happens during or soon after the sixth year. This first permanent tooth does not displace any of the milk teeth, but comes down behind the second milk molar

2. By the seventh year after the birth of a child, the central milk incisors fall out and their place is taken by the permanent central incisors.

3. By the eighth year after the birth of a child, the lateral incisors succeed their milk lateral incisors.

4. By the nineth year after the birth of a child, the first premolar takes the place of the first temporary molar.

5. By the tenth year after the birth of a child, the second premolar takes the place of that of the second temporary molar.

6. By the eleventh year after the birth of a child, the canine come out.

7. By the twelveth year after the birth of a child, the second molar comes down behind the first. It is therefore known as the twelve-year-old tooth.

8. Between eighteen and twenty year after the birth of a child, the third molar, or wisdom tooth, appears. This third molar, or wisdom tooth, may be come out much later. Sometimes this third molar, or wisdom tooth, may never come out at all, and when it does come, it often does not come down to a level with the other teeth.

Suppression of Last Molar Teeth

Observations by dentists and scientist suggests that man is gradually undergoing a suppression of his last molar teeth and this will lead to the distant future man having a different dental formula from our own.

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