dr. hoori mir mohammad sadeghi “in the name of god”

Dr. Hoori Mir Mohammad Sadeghi

“In the name of GOD”

Stages of dental development

• Gum pad stage

• Primary dentition stage

• Mixed dentition stage

• permanent dentition stage

From birth until eruption of primary first tooth, Usually lower central incisor around 6-7 month of age.

Primary dentition stage

Primary dentition

Dental development • 6 months ± 6

• Natal teeth, usually one of primary incisor which was erupted sooner.

• All of primary teeth usually erupt between 24 to 30 months.

Primary dentition stage

Calcification sequence

A-D-B-C-E

Eruption sequence

A B D C E• A B D C E

Spaced or a Closed dentitionSpaced dentition occurs in the maxilla in 70% of the patients and in the mandible in 63%.

Closed dentition exist in the maxillary dentition in 30% of the patients and none in the mandibular in 37%.

Spaced dentiotion

Closed dentiotion

A primary dentition without spacing is followed by crowding in the permanent dentition .

Contrary to widely held misconception, arch length is reduced after the premature loss of a primary incisor . This is particularly true if the incisor is lost early and the primary dentition is a closed dentition.

Molar relationship

Flush terminal plane Mesial step Distal step

ObjectivesObjectives

I. Eruption of the permanent dentition

II. Development of the molar occlusion

I. Eruption of the permanent dentition

II. Development of the molar occlusion

Development of the Occlusion Development of the Occlusion

ThemesThemes

a.Timing and Sequenceb. Incisor Replacementc. Leeway and E-space

a.Timing and Sequenceb. Incisor Replacementc. Leeway and E-space

EruptionEruption

Eruption Sequence/TimingEruption Sequence/Timing

Permanent DentitionPermanent Dentition

Age in yearsAge in years

Mx 6 1 2 4 5 3 7Mx 6 1 2 4 5 3 7

Mn 6 1 2 3 4 5 7 Mn 6 1 2 3 4 5 7 6y 7y 8y 9y 10y 11y 12y

Incisor ReplacementIncisor Replacement

Permanent IncisorsPermanent Incisors

Are 2-3.5 mm/quadrant wider than primary incisors =

incisor liability

Are 2-3.5 mm/quadrant wider than primary incisors =

incisor liability

Crowding ????????????

Incisor liability

Are 2-3.5 mm/quadrant wider than primary incisors


1. Normal spacing: developmental and primate

2. Labial eruption of permanent (maxillary) incisors & Increase in arch width across canines, these erupt buccally (max.>mand.; boys>girls)

3. Distal repositioning of canines in mandible.Incisors force mandibular canines distally into primate space




Solutions:Solutions:

IncisorsIdeally the primary spacing of the spaced primary dentition will

be sufficient, together with other factors, to allow for the favorable alignment of the succedaneous permanent incisors .

In closed primary dentitions the permanent mandibular lateral incisors emerge and the primary mandibular canines are moved laterally. Thus a space is created that enables the permanent maxillary lateral incisors to emerge into a favorable alignment. This is referred to as secondary spacing occurs when the permanent mandibular central incisors are emerging.

Primary spacing

Primate space

Developmental space

Developmental

Spaces between incisors Primate

Max: Mesial of canineMand: Distal of canine

Developmental

Spaces between incisors Primate

Max: Mesial of canineMand: Distal of canine

Primary DentitionPrimary DentitionCharacteristic Spacing:Characteristic Spacing:

Primary DentitionPrimary Dentition

Characteristic Spacing:Characteristic Spacing:

Spacing: 60-70% of childrenSpacing: 60-70% of children

Secondary spacing

Secondary spacing occurring when the permanent mandibular lateral incisors are emerging.

Secondary spacing

Secondary spacing occurring when the maxillary central incisors are emerging

Ectopic eruption of the permanent mandibular lateral incisors and its effect on

secondary spacing.

Increase arch perimeter by eruption with more labial inclination

Increase arch perimeter by eruption with more labial inclination

Canines Erupt BuccallyCanines Erupt Buccally

Canines Moved DistallyCanines Moved Distally








Solutions:Solutions:

Central DiastemaCentral Diastema

Closes with eruption of lateral incisorsCloses with eruption of lateral incisors

Maxillary Arch ≤ 2 mm,mixed dentitionMaxillary Arch ≤ 2

mm,mixed dentition

Close diastema for esthetics or to make room for laterals

If not ≈ ‘Ugly Duckling’ Stage and will close with

eruption of canines.

If not ≈ ‘Ugly Duckling’ Stage and will close with

eruption of canines.

Leeway space • The mandibular primary second molar is on the

average 2 mm larger than the second premolar, while in the maxillary arch, the primary second

molar is 1.5mm larger. The primary first molar is only slightly larger than the first premolar, but

does contribute an extra 0.5 mm in the mandible.

• The result is that each side in the mandibular arch

contains about 2.5mm of what is called leeway space, while in the maxillary arch,a bout

1.5mm is available on the average.

E-spaceE-space

If anterior crowding is present, send to orthodontist before primary 2nd molars exfoliate

If anterior crowding is present, send to orthodontist before primary 2nd molars exfoliate

Primary molar occlusion Developing permanent molar occlusion

Early mesial shift The prevalence of Class II decreases

Late mesial shiftDifferential growth

Primary molar occlusion Developing permanent molar occlusion

Early mesial shift The prevalence of Class II decreases

Late mesial shiftDifferential growth

Development of the Molar Occlusion

Development of the Molar Occlusion

PrimarySecondMolars

PrimarySecondMolars

Primary Molar Occlusion Primary Molar Occlusion

Mesial StepMesial Step

Distal StepDistal Step

Flush Terminal Plane

Flush Terminal Plane

AnteriorAnteriorPosteriorPosterior

The primary teeth relationships

1. Straight terminal plane(76%) most frequent occurring relationship, must be observed the most critically. Depending on a number of factors, the straight terminal plain can guide

the permanent molars into a normal Class I or an abnormal Class II relationship.

2. Mesial step(14%) The mesial step is an ideal relationship that routinely guides the permanent first molars into a favorable Class I intercuspation.

3. Distal step (10%)The distal step, as a rule, guides the permanent first molars into an abnormal Class II malocclusion.

First molars Several situations can exist for the permanent first molars. In

patients with a spaced primary dentition and a straight terminal plane relationship of the primary molars, the permanent mandibular first molars emerge at about 6 years, move the primary molars mesially, close the space distal to the primary canines, convert the straight terminal plane to a mesial step relationship, reduce arch length in the mandibular dentition, and allow the permanent maxillary molars to emerge into a Class I relationship. This has been referred to as the early mesial shift .

The early mesial shift

Early Mesial Shift Early Mesial Shift

If mandibular primate space is available during eruption of permanent 1st molar Flush terminal plane to mesial step What age?

If mandibular primate space is available during eruption of permanent 1st molar Flush terminal plane to mesial step What age?

Permanent Molar Occlusion Permanent Molar Occlusion

Mesial StepMesial Step

Distal StepDistal Step

Flush Terminal PlaneFlush Terminal Plane

Class I

Class II

Class II

The late mesial shift

After permanent dentition is completeAfter permanent dentition is complete

Final occlusionFinal occlusion

DD MM

Molar Occlusion Molar Occlusion

85 pairs (42%) initial occlusion cusp to cusp

85 pairs (42%) initial occlusion cusp to cusp

66%66%

26%26%

8%8%

DD MM

Late Mesial Shift Late Mesial Shift Leeway SpaceMandibular molars may move mesially more than maxillary molars

Leeway SpaceMandibular molars may move mesially more than maxillary molars

Differential GrowthWhen is the growth spurt occuring?

Females?Males?

Differential GrowthWhen is the growth spurt occuring?

Females?Males?

Differential Growth Differential Growth

The basis of differential growth:

mandibular growth reflects general growth more than maxillary growth does

The basis of differential growth:

mandibular growth reflects general growth more than maxillary growth does

OverbiteOverbite is related to the growth of the jaws and the rate of

eruption of the incisor teeth.

Overbite increases from the primary dentition to the permanent.

According to Baume, 40% of primary dentitions have a slight overbite.

Arch dimensions• According to Baume, arch dimension

does not change during the primary dentition: arch length does not change in the maxilla and mandible in most of the cases; arch width does not change in the maxilla and mandible in most of the cases .

Mixed dentition. • At present, overwhelming scientific evidence indicates that the

posterior teeth move forward throughout life. This tends to reduce arch length.

• Moorrees has established that arch length decreases 2 to 3 mm between 10 and 14 years, when the primary molars are being replaced by the permanent premolars .

• He also has demonstrated that the arch circumference is reduced about 3.5 mm in the mandible of boys and 4.5 mm in girls during the mixed dentition period.

Reduction in arch length as a result of the moving forward of posterior teeth

Arch Depth

Why arch length decrease?

In newborn infants the tongue tends to fill the oral cavity and often

encroaches on the alveolar ridge area. As a consequence of the more

rapid anterior growth of the jaws in the postnatal period, the tongue

lags behind and comes to occupy a more posterior position in the oral

cavity. This is consistent with the upright positioning of the incisors

that occurs in many adolescents.

Arch length decreases from the anterior and the posterior side.

Upright positioning of incisors with forward growth

If extensive inter proximal caries is allowed to develop in the maxilla, a similar situation will occur: a reduction of arch length causing crowding.

Primary maxillary second molarsIf the caries is so extensive that extraction of the primary maxillary second

molars is necessary, again crowding will result.

Primary maxillary first molars

Similarly, and this is contrary to popular belief, premature loss of the primary maxillary first molars will cause crowding .

Ectopic eruptionEctopic eruption of the permanent maxillary first molars, resulting in premature exfoliation of the primary second molars and loss of arch length, indicates a lack of development of the tuberosity. This results in not only crowding but also a Class II molar relationship.

Premature loss of primary second maxillary molars

If the exfoliation sequence of the primary second molars is reversed and the maxillary molar is lost before the mandibular, a Class II relationship of the permanent first molars will result. Again, arch length will be reduced, and crowding will occur in the maxilla.

Premature loss of primary second mandibular molars

If the primary mandibular second molar is lost far too early, the mandibular arch length will be reduced to such an extent that the normal leeway wiII be exceeded and crowding will occur.

dr. hoori mir mohammad sadeghi “in the name of god”

Documents

primary dentition stage

eruption of primary

primary incisors

spaced primary dentition

incisors primary spacing

maxillary dentition

incisor liability slide

primary teeth