Dr. Hoori Mir Mohammad Sadeghi “In the name of GOD” Dr. Hoori Mir Mohammad Sadeghi

Stages of dental development Gum pad stage Primary dentition stage Mixed dentition stage permanent dentition stage

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

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 dentition Spaced 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

Development of the Occlusion Objectives Eruption of the permanent dentition II. Development of the molar occlusion

Eruption Themes Timing and Sequence Incisor Replacement Leeway and E-space

Permanent Dentition Eruption Sequence/Timing Mx 6 1 2 4 5 3 7 Mn 6 1 2 3 4 5 7 6y 7y 8y 9y 10y 11y 12y Age in years

Are 2-3.5 mm/quadrant wider than primary incisors = incisor liability Incisor Replacement Permanent Incisors Are 2-3.5 mm/quadrant wider than primary incisors = incisor liability

Crowding. Incisor liability Are 2-3 Crowding ???????????? Incisor liability Are 2-3.5 mm/quadrant wider than primary incisors

Incisor Replacement Solutions: Normal spacing: developmental and primate Labial eruption of permanent (maxillary) incisors & Increase in arch width across canines, these erupt buccally (max.>mand.; boys>girls) Distal repositioning of canines in mandible. Incisors force mandibular canines distally into primate space

Incisors Ideally 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

Primary Dentition Developmental Primate Characteristic Spacing: Spaces between incisors Primate Max: Mesial of canine Mand: Distal of canine

Primary Dentition Characteristic Spacing: Spacing: 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

Canines Erupt Buccally

Canines Erupt Buccally

Canines Moved Distally

Incisor Replacement Solutions: Normal spacing: developmental and primate Labial eruption of permanent (maxillary) incisors & Increase in arch width across canines, these erupt buccally (max.>mand.; boys>girls) Distal repositioning of canines in mandible. Incisors force mandibular canines distally into primate space

Maxillary Arch ≤ 2 mm,mixed dentition Central Diastema Maxillary Arch ≤ 2 mm,mixed dentition Closes with eruption of lateral incisors If not ≈ ‘Ugly Duckling’ Stage and will close with eruption of canines. Close diastema for esthetics or to make room for laterals

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

Development of the Molar Occlusion Primary molar occlusion Developing permanent molar occlusion Early mesial shift The prevalence of Class II decreases Late mesial shift Differential growth

Primary Molar Occlusion Mesial Step Distal Step Flush Terminal Plane Primary Second Molars Posterior Anterior

The primary teeth relationships 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. Mesial step(14%) The mesial step is an ideal relationship that routinely guides the permanent first molars into a favorable Class I intercuspation. 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 If mandibular primate space is available during eruption of permanent 1st molar Flush terminal plane to mesial step What age?

Permanent Molar Occlusion Mesial Step Distal Step Flush Terminal Plane Class I Class II

The late mesial shift

Molar Occlusion Final occlusion D M D M 66% 26% 8% 85 pairs (42%) initial occlusion cusp to cusp After permanent dentition is complete

Late Mesial Shift Leeway Space Mandibular molars may move mesially more than maxillary molars Differential Growth When is the growth spurt occuring? Females? Males?

Differential Growth The basis of differential growth: mandibular growth reflects general growth more than maxillary growth does

Overbite Overbite 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 molars If 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 eruption Ectopic 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.