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IDENTIFY ANDDESCRIBE THEPRIMARY AND

MIXEDDENTITIONS

1. TITLE SLIDE: IDENTIFY AND DESCRIBE THEPRIMARY AN DMIXED DENTITIONS In this presentation, you willreview the differences between the primary and permanent dentitions. You willlearn to recognize when each are present, or when both are present as a mixeddentition.

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The Primary Dentition

2. A child's first set of teeth is called the primary dentition. Theteeth in the primary dentition are called primary teeth. Primary teeth are alsocalled baby teeth, milk teeth, temporary teeth or deciduous teeth. (In Latin,decidere means to fall off or be shed, like leaves from a tree). As the termdeciduous implies, the primary teeth are replaced by permanent teeth. However,this fact does not diminish the importance of the primary teeth; they areimportant to the child's present and future oral health and general well being.This picture illustrates the ideal primary dentition. Note the appropriate spacing,this allows for the larger teeth in the permanent dentition to have adequate roomduring eruption. The spacing also allows for natural self-cleansing inside themouth.

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The Primary Dentition

Central Incisor

Lateral Incisor

Canine

First Molar

Second Molar

3. The primary dentition consists of twenty teeth. As illustrated inthe slide on the right, each quadrant contains two incisors, one canine and twomolars. The types and arrangement of the primary teeth are illustrated in thefigure on the left. Notice the lack of premolars in the primary dentition. (LifeArt image

copyright 1999 Lippincott Williams & Wilkins. All rights reserved.)

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Primary Teethvs.

Permanent TeethPrimary and Permanent teeth differ in:Primary and Permanent teeth differ in:

SizeSize

NumberNumber

Time of eruptionTime of eruption

MorphologyMorphology

Color andColor and

Root formRoot form

4. This slide highlights some of the major differences between theprimary and permanent dentition.

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Primary Teeth vs. Permanent TeethSize, Number and Arch Alignment

5. The teeth in the primary dentition are smaller and fewer innumber than the teeth in the permanent dentition. There are only twenty primaryteeth. They tend to be wider, shorter and whiter. The arches of the primarydentition have an ovoid shape. This is in contrast to the permanent dentitionwhich is more elliptical in shape. (LifeArt image copyright 1999 Lippincott Williams & Willkins. All rights reserved.)

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Primary Tooth MorphologyPrimary teeth: lighter in color smaller than permanent teeth

crowns are shorter & wider more convex at the CEJ occlusal anatomy is not as well defined

dentin and enamel are thinner

pulp chamber is larger roots are longer, thinner, &

flatter. Posterior roots are more flared to allow

for developing permanent teeth.

6. This slide lists several differences that distinguish the primaryteeth from the permanent teeth.

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Anatomy of Primary MaxillaryAnterior Teeth

Incisal viewIncisal view

Labial viewLabial view

7. The mesiodistal width of the crown of the maxillary anteriorteeth is greater than the incisocervical length, giving the teeth a squattyappearance. This appearance is characteristic of all the primary anterior teethand makes them dissimilar to their permanent successors. The labial surfaces ofthe maxillary incisors are very smooth and the incisal edges are nearly straight.The labial surface of the maxillary canine does not resemble either of theincisors. The crown is more constricted at the cervix and the mesial and distalsurfaces are more convex. It has a well-developed cusp instead instead of anincisal edge. The contact areas are level with each other; contact areas are not atthe same level on permanent canines. (Images courtesy UK College of Dentistry; Department of Pediatric Dentistry. )

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Anatomy of Primary MandibularAnterior Teeth

Incisal viewIncisal view

Labial viewLabial view

IntercuspationIntercuspation of ofprimary caninesprimary canines

8. The labial surface of the primary mandibular incisors are alsosmooth and flat with no developmental markings. The mandibular centralincisors are smaller than the lateral incisors. The functional design of theprimary mandibular canine is similar to the maxillary canine. One variation isthe slope of the cusp: longest cusp slope on the mandibular canine is on thedistal. This is opposite to that of the maxillary canine; the longest cusp slope isto the mesial. This design makes for proper intercuspation of these teeth when inocclusion. (Images courtesy UK College of Dentistry; Department of Pediatric Dentistry.)

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Root Anatomy of PrimaryAnterior Teeth

Crown-to-root ratio forCrown-to-root ratio formaxillary central incisorsmaxillary central incisors

Primary MaxillaryPrimary MaxillaryCentral IncisorCentral Incisor

9. The roots of the anterior primary teeth are cone-shaped withevenly tapered sides. The root lengths are greater in comparison to the crownlengths than in the permanent teeth. (Image courtesy UK College of Dentistry; Department of Pediatric Dentistry.)

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Occlusal Anatomy of MaxillaryPrimary First Molar Compared to

First Permanent Molar

10. The crown size and occlusal anatomy of the posterior primaryteeth differ from their permanent counterparts. In general, the occlusal anatomyof primary teeth is not as well defined as that of the permanent teeth. Theocclusal ridges and cusps are shallow. The crown of the primary first molar doesnot resemble any other tooth in either the primary or permanent dentitions. Thecrown is triangular in shape and may have four cusps; however it typically hasonly three cusps because the distolingual cusp is missing.. The occlusal table hasa very prominent oblique ridge connecting the mesiolingual cusp with thedistobuccal cusp.

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Occlusal Anatomy of MaxillaryPrimary Second Molar Compared

to First Permanent Molar

11. The occlusal anatomy of a primary maxillary second molarresembles a permanent maxillary first molar, except that it is smaller. It has fourwell developed cusps and a fifth supplemental cusp. The developmental grooves(pits and fissures) and ridges are less defined, but are almost identical to thosefound on a permanent first molar. (Slide courtesy UK College of Dentistry; Department of Pediatric Dentistry.)

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Occlusal Anatomy of MandibularPrimary First Molar Compared to

First Permanent Molar

12. A primary mandibular first molar does not resemble any othertooth in either the primary or permanent dentitions. The mesiobuccal cervicalridge is very prominent and gives the outline of the crown a rhomboidal shapethat tapers distally.

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Occlusal Anatomy of MandibularPrimary Second Molar Compared

to First Permanent Molar

13. The occlusal anatomy of a primary mandibular second molarresembles that of the permanent first molar except that all three buccal cusps aresimilar in size and development. In contrast, the distal cusp of the permanentmolar is smaller than the other two cusps. (Slide courtesy UK College of Dentistry; Department of Pediatric Dentistry.)

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Root Anatomy of Primary MolarsCompared to Permanent Molars

PermanentPermanentmolarmolar

PrimaryPrimarymolarmolar

14. The roots of the posterior primary teeth are more flared thanthose of the posterior permanent teeth. This flaring provides space for thedeveloping succedaneous (the premolar) tooth bud to develop. (Slides courtesy UK College of

Dentistry; Department of Pediatric Dentistry.)

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There is usually generalizedThere is usually generalizedspacing among the anteriorspacing among the anteriorteeth.teeth.

Spacing ranges from 0-10 mmSpacing ranges from 0-10 mmin the maxillary arch, with anin the maxillary arch, with anaverage of 4 mm.average of 4 mm.

Spacing ranges from 0-6 mm inSpacing ranges from 0-6 mm inthe mandibular arch with anthe mandibular arch with anaverage of 3 mm.average of 3 mm.

Spacing is normal & desirable;Spacing is normal & desirable;it helps overcome the significantit helps overcome the significantsize differential between thesize differential between theprimary & permanent incisors.primary & permanent incisors.

Characteristics of the Primary Dentition- Developmental Spacing

15. As the jaws of the child continue to grow, slight spaces arecreated between some of the teeth. There is usually generalized spacing betweenthe anterior teeth in the primary dentition. This spacing is normal and desirable;it helps overcome the significant size differential between the primary andpermanent incisors. There are two types of spacing identified in the primarydentition. The generalized spacing between the teeth is referred to asdevelopmental spacing. (Slide courtesy UK College of Dentistry; Department of Pediatric Dentistry.)

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Characteristics of the Primary Dentition- Primate Spacing

16. The space located mesial to the maxillary canine and distal to themandibular canine is referred to as the primate space. The primate space is thespace that the canine of the opposing arch occludes into. This space is referredto as the primate space because it is typically found in the dentitions of allprimates (monkeys, apes and humans). (Slides courtesy UK College of Dentistry; Department of Pediatric Dentistry.)

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Eruption Time Table– Primary Teeth

17. The first primary tooth comes in at about 6 months of age and the20th and last primary tooth erupts at around 2 1/2 years of age. Dates areaverages and do have standard deviations. Time of arrival of the teeth is of noparticular significance unless it deviates significantly. More important whenevaluating the eruption of the primary dentition is the eruption sequence andpattern on both sides of the mouth. Teeth tend to erupt in pairs, on both the rightand left sides of the arches. The mandibular teeth usually precede the maxillaryin eruption, usually by one-two months. Children with delayed eruption mayhave either a very slow, but normal eruption or some isolated eruption problems.To distinguish the two, the child’s eruption sequence is evaluated with normalsequence of eruption and the eruption pattern on the right side is compared tothat on the left. If the sequence seems normal, eruption is probably slow.However, if the eruption sequence of the teeth deviates from normal and thereare differences on contra-lateral sides of the mouth, further evaluation isnecessary to determine if teeth are missing or are impeded from erupting.

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Bruxism

FacialFacial ViewView MaxillaryMaxillaryOcclusal ViewOcclusal View

18. Generally, all of the primary teeth have erupted and are inocclusion by the time the child is three years of age. The natural spacing of teethcaused by jaw growth opens up contacts between the teeth, causing migration ofteeth. The stable cusp-to-fossa relationship seen in the permanent occlusion doesnot develop in the primary dentition. Since the teeth do not hold their stablepositions, occlusal wear is increased. The teeth are worn off rapidly on incisaledges and occlusal surfaces. For example, when the primary canine is lost 8years or more after its eruption, the long, sharp cusp has most often lost beenworn down. However, this bruxism does not adversely affect the oral health ofthe child.

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Eruption of Permanent TeethPermanent 1Permanent 1stst molars molars

19. The first teeth of the permanent dentition to erupt into the oralcavity are the first molars. They erupt immediately distal to the primary secondmolars at about age 6. Therefore, these teeth are often called the “six yearmolars”. They are larger than any of the primary teeth and cannot erupt until thejaw growth has progressed sufficiently to allow the space.

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Exfoliation of Primary ToothYields to a Permanent Tooth

20. The second permanent tooth to emerge into the oral cavity is themandibular central incisor. Before the permanent central incisor can come intoposition, the primary central incisor must be exfoliated. This occurs by thephenomenon called resorption of the primary roots. As a permanent toothdevelops in its follicle, the root begins to form and the tooth begins to force itsway into the position held by its predecessor. The developing permanent toothwill begin to apply a pressure on the root of the primary tooth. This pressurecauses the root of the primary tooth to resorb. Root resorption of the primarytooth continues until the tooth has lost its anchorage and becomes mobile, and isfinally exfoliated. The open space allows the permanent tooth to erupt intoproper position in the mouth. (LifeArt image copyright 1999 Lippincott Williams & Willkins. All rights reserved.)

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Exfoliation Time Table– Primary Teeth

(Tooth Fairy Visits)

21. This chart gives the approximate dates that the primary teeth arelost to make way for their permanent successors. This exfoliation chart onlyprovides general guidelines. There is great variation in the eruption andshedding of the primary teeth.

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Permanent Teeth ReplacePrimary Teeth

nonethird molar

nonesecond molar

nonefirst molar

second molarsecond premolar

first molarfirst premolar

caninecanine

lateral incisorlateral incisor

central incisorcentral incisor

Primary TeethPermanent Teeth

22. The eruption sequence of the permanent teeth begins around agesix and continues until approximately age twelve. This chart shows whichpermanent teeth replace which primary teeth. Note that the permanent molars donot replace any primary teeth. They are non-succedaneous teeth.

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Average Age of Eruption– Permanent Teeth

23. This chart reviews the average age of eruption for the permanentteeth into the oral cavity. Again, there can be significant variation betweenchildren.

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Eruption of PermanentAnterior Teeth

24. As shown in this view of the skull, the follicles of the developingpermanent incisors and canines are in a position lingual to the roots of theprimary anterior teeth. The slide on the right shows eruption of a permanentincisor lingual to the primary incisor. The appearance of the permanent incisorin the mouth lingual to the primary incisor is fairly common, the primary toothwill soon be lost due to root resorption and loss of support, allowing thepermanent successor to move into proper position.

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Arrangement of DevelopingPermanent Teeth in the Jaw

25. The developing premolars take the place of the primary molarsand are located within the bifurcation of the primary molar roots. This model ofa lateral view of the primary dentition and developing permanent dentitionillustrates the development of the premolar tooth buds in the furcation areas ofthe primary molars.

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26. These radiographs also illustrate the development and eruption ofthe permanent premolars. The panoramic radiograph illustrates the position ofthe premolars in the furcation areas of the primary roots. In the bitewingradiographs, notice how the roots of the primary teeth are resorbing to aid inexfoliation and eruption of the permanent premolars. In the bitewing radiographon the left, you can see the primary molars right before they are lost.

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The Mixed Dentition

27. The period when both primary and permanent teeth are present inthe oral cavity is called the mixed dentition period. This is an intraoral picture ofa child approximately eight years of age.

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The “Ugly Duckling” Stage

28. This transient stage is sometimes referred to as the “uglyduckling” stage due to the extra spacing and the size variation among the teeth.

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The Mixed Dentition

29. These diagrams show the primary teeth in yellow and thepermanent teeth in green at three different ages in a child’s development. Notethe positioning of the primary and permanent teeth during eruption and theirposition in relation to each other.

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The Importance of Primary Teeth

30. All of the primary teeth are in use from the age of 2 until the ageof 7 (5 years in all). Some of the primary teeth are in use from 6 months until 12years of age (11½ years in all). It is very important that primary teeth are kepthealthy until they are lost naturally. They serve a number of important functions.They help maintain good nutrition by permitting the child to chew properly.They are important in allowing good pronunciation and speech habits; and theyhelp the child feel good about the way he/she looks to others. Primary teeth alsomaintain space for the permanent teeth developing underneath them in the jawsand help guide the proper eruption of the permanent teeth.

This completes the slide presentation.