7Spaced 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%.
9A 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.
15Crowding. Incisor liability Are 2-3 Crowding ???????????? Incisor liability Are mm/quadrant wider than primary incisors
16Incisor Replacement Solutions: Normal spacing: developmental and primateLabial 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
17IncisorsIdeally 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.
31Incisor Replacement Solutions: Normal spacing: developmental and primateLabial 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
32Maxillary Arch ≤ 2 mm,mixed dentition Central DiastemaMaxillary Arch ≤ 2 mm,mixed dentitionCloses with eruption of lateral incisorsIf not ≈ ‘Ugly Duckling’ Stage and will close with eruption of canines.Close diastema for esthetics or to make room for laterals
33Leeway spaceThe 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.
34E-spaceIf anterior crowding is present, send to orthodontist before primary 2nd molars exfoliate
35Development of the Molar Occlusion Primary molar occlusionDeveloping permanent molar occlusion Early mesial shiftThe prevalence of Class II decreases Late mesial shift Differential growth
36Primary Molar Occlusion Mesial StepDistal StepFlush Terminal PlanePrimary Second MolarsPosteriorAnterior
37The 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.
39First molarsSeveral 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 .
52OverbiteOverbite 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.
53Arch dimensionsAccording 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 .
55Mixed 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.
56Reduction in arch length as a result of the moving forward of posterior teeth
58Why 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.
59Upright positioning of incisors with forward growth
60If extensive inter proximal caries is allowed to develop in the maxilla, a similar situation will occur: a reduction of arch length causing crowding.
61Primary maxillary second molars If the caries is so extensive that extraction of the primary maxillary second molars is necessary, again crowding will result.
62Primary maxillary first molars Similarly, and this is contrary to popular belief, premature loss of the primary maxillary first molars will cause crowding .
63Ectopic 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.
64Premature 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.
65Premature 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.