THE DECIDUOUS DENTITION / Importance of the Deciduous Dentition

 

I. The Deciduous Dentition

-It is also known as the primary, baby, milk or lacteal dentition.

 

A. Overview. You will recall that we are diphyodont, that is, with two sets of teeth. The term deciduous means literally 'to fall off.'

-There are twenty deciduous teeth that are classified into three classes. Do you recall the term heterodont? There are ten maxillary teeth and ten mandibular teeth. The dentition consists of incisors, canines and molars.

-The dental formula is as follows.

-The notation for deciduous teeth is A though J, K through T. It is 'clockwise'just like it is for permanent teeth as you look at the patient from in front.

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B. Role in development. A person 70 years old will have spent 91% of his/her life chewing on permanent teeth, but only 6% of his/her chewing career with the deciduous dentition.

-Although the deciduous teeth are in time replaced by the succedaneous teeth, the deciduous teeth play a very important role in the proper alignment, spacing, and occlusion of the permanent teeth.

-The deciduous incisor teeth are functional in the mouth for approximately five years, while the deciduous molars are functional for approximately nine years. They therefore have considerable functional significance. When second deciduous molars are lost prematurely, this can be very detrimental to the alignment of the permanent teeth.

Development of the Deciduous Dentition

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II. Formation and Eruption of Deciduous Teeth.

-Calcification begins during the fourth month of fetal life. By the end of the sixth month, all of the deciduous teeth have begun calcification.

-Clinical hint: good nutrition is essential.

-By the time the deciduous teeth have fully erupted (two to two and one half years of age), cacification of the crowns of permanent teeth is under way. First permanent molars have begun cacification at the time of birth. Clinical hint: with deciduous molars, extract with caution.

-Here are some things to know about eruption patterns:

(1) Teeth tend to erupt in pairs. Clinical hint: look for asymmetry. Take an X-ray film as required.

 

(2) Usually, lower deciduous teeth erupt first. Congenitally missing deciduous teeth is infrequent. Usually, the lower deciduous central incisors are thefirst to erupt thus initiating the deciduous dentition. The appearance of the deciduous second molars completes the deciduous dentition by 2 to 2 1/2 years of age.

-Comment: Eruption dates are variable. Some infants get them early, others do so late. If the teeth are unduly early or late, you should inquire about siblings, or the parents themselves. Timing of eruption 'runs in families.'

-Comment: Deciduous teeth shed earlier and permanent teeth erupt earlier in girls.

-Comment: The orderly pattern of eruption and their orderly replacement by permanent teeth is important.

-The textbook order for eruption of the deciduous teeth is as follows:

(1) Central incisor.........Lower 6 ½ months, Upper 7 ½ months

(2) Lateral incisor.........Lower 7 months, Upper 8 months

(3) First deciduous molar...Lower 12-16 months, Upper 12-16 months

(4) Deciduous canine........Lower 16-20 months, Upper 16-20 months

(5) Second deciduous molar..Lower 20-30 months, Upper 20-30 months

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III. Root Formation and Obliteration

A. In general, the root of a deciduous tooth is completely formed in just about one year after eruption of that tooth into the mouth.

B. The intact root of the deciduous tooth is short lived. The roots remain fully formed only for about three years.

C. The intact root then begins to resorb at the apex or to the side of the apex, depending on the position of the developing permanent tooth bud.

D. Anterior permanent teeth tend to form toward the lingual of the deciduous teeth, although the canines can be the exception. Premolar teeth form between the roots of the deciduous molar teeth.

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IV. The Transition from the Deciduous to the Permanent Dentition.

A. The transition begins with the eruption of the four first permanent molars, and replacement of the lower deciduous central incisors by the permanent lower central incisors.

B. Complete resorption of the deciduous tooth roots permits exfoliation of that tooth and replacement by the permanent (successional) teeth.

C. The mixed dentition exists from approximately age 6 years to approximately age 12 years. In contrast, the intact deciduous dentition is functional from age 2 - 2 /2 years of age to 6 years of age.

 

D. The enamel organ of each permanent anterior tooth is connected to the oral epithelium via a fibrous cord, the gubernaculum. The foramina through which it passes can be seen in youthful skulls......

V. The Importance of the Deciduous Dentition.

A. It is what the child chews, speaks, and smiles with during his/her formative years. The functional and esthetic importance of these teeth is self evident. The challenge for the clinician lies in communicating with dollar conscious parents who say: "those are just baby teeth. They will just fall out soon."

B. As a rule, these teeth should be restored and preserved until their normal time of exfoliation. This statement especially applies to second molars.

C. The deciduous second molars are particularly important. It is imperative that the deciduous second molars be preserved until their normal time of exfoliation. This prevent mesial migration of the first permanent molars. Clinical hint: Use a space maintainer in the event that a second deciduous molar is lost prematurely.

-Comment: After the age of nine or so, you may extract any of the deciduous teeth with impunity except those second deciduous molars we have been talking about. Physiological mesial drift is not significant in the deciduous dentition. Besides, succedaneous teeth are on the way.

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VI. Differences Between the Deciduous and Permanent Teeth

-Comment: Listen up! These are 'pet' questions for our and for National Boards examinations.

A. Deciduous teeth are fewer in number and smaller in size but the deciduous molars are wider mesiodistally than the premolars. The deciduous anteriors are narrower mesiodistally than their permanent successors. Remember the leeway space that we discussed in the unit on occlusion?

B. Their enamel is thinner and whiter in appearance. Side by side, this is obvious in most young patients.

C. The crowns are rounded. The deciduous teeth are constricted at the neck (cervix).

D. The roots of deciduous anterior teeth are longer and narrower than the roots of their permanent successors.

E. The roots of deciduous molars are longer and more slender than the roots of the permanent molars. Also, they flare greatly.

F. The cervical ridges of enamel seen on deciduous teeth are more prominent than on the permanent teeth. This 'bulge' is very pronounced at the mesiobuccal of deciduous first molars.

G. Deciduous cervical enamel rods incline incisally/occlusally.

..... MORPHOLOGY OF THE DECIDUOUS TEETH

VII. Deciduous Anterior Teeth.

 

-The primary anteriors are morphologically similar to the permanent anteriors.

-The incisors are relatively simple in their morphology.

-The roots are long and narrow.

-When compared to the permanent incisors, the mesiodistal dimension is relatively larger when compared to axial crown length. In other words, they look 'squatty,' especially when worn.

-At the time of eruption, mamelons are not present in deciduous incisors. (Did you catch that?)

-They are narrower mesiodistally than their permanent successors.

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 VIII. Maxillary First Deciduous Molar.

 

-The notation is B or I.

-It looks a bit like an upper 1st premolar.

-There are three roots.

-It has a strong bulbous enamel bulge that protrudes buccally at the mesial.

-It is the smallest of the deciduous molars in crown height and in the mesiodistal dimension.

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IX. Maxillary Second Deciduous Molar.

-The notation is A or J.

-It looks like a first permanent molar

-There are three roots.

-Usually it has four well developed cusps.

-It is somwhat rhomboidal in outline.

-They often have the Carabelli trait.

-Studies have shown that the shape the maxillary first permanent molar strongly resembles that of the adjacent deciduous second molar.

Upper Row: Upper First Molar

Lower Row: Upper Second Molar

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X. Mandibular First Deciduous Molar.

 

-The notation is L or S.

-This tooth doesn't resemble any other tooth. It is unique unto itself.

-There are two roots.

-There is a strong bulbous enamel bulge buccally at the mesial.

-A favorite National Board question asks that you know about the cusps. The thing to remember is that the mesiolingual cusps on this tooth is the highest and largest of the cusps.

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XI. Mandibular Second Deciduous Molar.

-The notation is K or T.

-This tooth resembles the lower first permanent molar that is distal to it in the dental arch.

-There are two roots and five cusps. The three buccal cusps are all about the same size. This is in contrast to the lower first molar where the 'distal' cusp is smaller that the mesiobuccal and distobuccal cusps.

-The distal of the three buccal cusps may be shifted of onto the distal marginal ridge.

Upper Row: Lower First Molar

Lower Row: Lower First Molar

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X. Summary

-Upper molars have three roots, lowers have two roots.

-Upper and lower second deciduous molars resemble first permanent molars in the same quadrant.

-Upper first deciduous molars vaguely resemble upper premolars. -Lower first deciduous molars are odd and unique unto themselves.

-First deciduous molars (upper and lower) have a prominent bulge of enamel on the buccal at the mesial. These help in determining right and left. (Incidentally, there is a somewhat similar bulge of enamel seen on the permanent lower second molar. It is helpful in determining right and left.)

CJ '98