dr. hoori mir mohammad sadeghi “in the name of god”
TRANSCRIPT
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Dr. Hoori Mir Mohammad Sadeghi
“In the name of GOD”
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Stages of dental development
• Gum pad stage
• Primary dentition stage
• Mixed dentition stage
• permanent dentition stage
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From birth until eruption of primary first tooth, Usually lower central incisor around 6-7 month of age.
Primary dentition stage
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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.
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Primary dentition stage
Calcification sequence
A-D-B-C-E
Eruption sequence
A B D C E• A B D C E
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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%.
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Spaced dentiotion
Closed dentiotion
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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.
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Molar relationship
Flush terminal plane Mesial step Distal step
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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
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ThemesThemes
a.Timing and Sequenceb. Incisor Replacementc. Leeway and E-space
a.Timing and Sequenceb. Incisor Replacementc. Leeway and E-space
EruptionEruption
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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
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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
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Crowding ????????????
Incisor liability
Are 2-3.5 mm/quadrant wider than primary incisors
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Incisor ReplacementIncisor Replacement
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
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:
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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.
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Primary spacing
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Primate space
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Developmental space
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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:
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Primary DentitionPrimary Dentition
Characteristic Spacing:Characteristic Spacing:
Spacing: 60-70% of childrenSpacing: 60-70% of children
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Secondary spacing
Secondary spacing occurring when the permanent mandibular lateral incisors are emerging.
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Secondary spacing
Secondary spacing occurring when the maxillary central incisors are emerging
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Ectopic eruption of the permanent mandibular lateral incisors and its effect on
secondary spacing.
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Increase arch perimeter by eruption with more labial inclination
Increase arch perimeter by eruption with more labial inclination
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Canines Erupt BuccallyCanines Erupt Buccally
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Canines Erupt BuccallyCanines Erupt Buccally
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Canines Moved DistallyCanines Moved Distally
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Incisor ReplacementIncisor Replacement
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
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:
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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.
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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.
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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
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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
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PrimarySecondMolars
PrimarySecondMolars
Primary Molar Occlusion Primary Molar Occlusion
Mesial StepMesial Step
Distal StepDistal Step
Flush Terminal Plane
Flush Terminal Plane
AnteriorAnteriorPosteriorPosterior
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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.
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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 .
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The early mesial shift
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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?
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Permanent Molar Occlusion Permanent Molar Occlusion
Mesial StepMesial Step
Distal StepDistal Step
Flush Terminal PlaneFlush Terminal Plane
Class I
Class II
Class II
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The late mesial shift
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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
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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?
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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
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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.
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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 .
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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.
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Reduction in arch length as a result of the moving forward of posterior teeth
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Arch Depth
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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.
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Upright positioning of incisors with forward growth
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If extensive inter proximal caries is allowed to develop in the maxilla, a similar situation will occur: a reduction of arch length causing crowding.
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Primary maxillary second molarsIf the caries is so extensive that extraction of the primary maxillary second
molars is necessary, again crowding will result.
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Primary maxillary first molars
Similarly, and this is contrary to popular belief, premature loss of the primary maxillary first molars will cause crowding .
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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.
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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.
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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.
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