Development of Dentition & Occlusion

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Development of Dentition and Occlusion

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From birth until adulthood and beyond dental occlusion undergoes significant changes Drastic in Mixed Dentition stage Subtle/slow in early and late adulthood stage

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Stages of Dental Development Gum Pad Stage Primary Dentition Stage Mixed Dentition Stage Permanent Dentition Stage

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Gum Pad stage A. Mouth of Neonate At birth the alveolar processes are covered by gum pads which soon gets segmented to indicate the site of developing teeth Clinical Significance Identification of Delayed eruption Ano/oligodontia Relationship of neonatal gum pads is a poor indicator of future dental relations r=0.4

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Natal,Neonatal & Pre-erupted Teeth Natal Teeth (Present at Birth) Neonatal Teeth (Erupted during the 1 st month) Pre-erupted (Erupting during the 2 nd & 3 rd month) Clinical Significance Difficulty to mother during breast feeding Remove only if they are superneumeraries or if they are loose enough that there is danger of exfoliation

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One week old boy with two neonatal teeth

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Primary Dentition Stage Extends from the eruption of 1 st primary teeth i.e. primary lower central incisor (6-7 months) until the eruption of the 1 st permanent tooth around 6 yrs of age

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Calcification Sequence of initial calcification of the primary teeth is Central incisor 14weeks 1 st molars 15 weeks Lateral incisor 16 weeks Canines 17 weeks 2 nd molars 18 weeks

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Eruption Timings Maxillary Teeth Time of eruption in months A 08 B 09 C 18 D 14 E 24 Mandibular Teeth Time of eruption in months A 06 B 07 C 16 D 14 E 20 + 6 months

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Sequence of Eruption _ A B _ D C _ E A B D C E Eruption timings varies + 6 months

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Clinical Significance Anomalies of crown dev. are seen less frequently in primary dentition Congenitally missing teeth less frequent Variations in size, shape & sequence of eruption also less frequent in primary dentition Primary teeth are more likely to be involved and lower teeth twice as often as upper , compared to permanent teeth. Primary molars quiet frequently gets fused Teething & Systemic Disturbances

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Features of Primary Dentition In early stages of development tongue plays an important role in shaping the arches but its role diminishes with age. Spaced anteriors Primate spaces Shallow overjet & overbite Class I molar relationship Flush terminal plane Primary mandibular 2nd is wider then maxillary 2 nd molar Vertical inclination of anteriors Ovoid arch shape

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Spacing It is important to have spacing in the deciduous teeth as Crowding in deciduous dentition -----crowding in permanent dentition Normal alignment of dec. dentition----2/3 rd will be with crowding in P.D Spacing < 3mm in dec. dentition------1/2 will be with crowding in P.D Spacing b/w 3-6 mm ------------- 1/5 th will be with crowding in P.D Spacing > 6 mm ------------------very little chance that child in permanent dentition will develop crowding

Spaced Anteriors:

Spaced Anteriors

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Molar Relationship In flush terminal plane relationship, both the maxillary and mandibular planes are at the same level anterio-posteriorly However mesial step and distal step are also seen in the primary dentition though less frequently In the mesial step relationship, the maxillary terminal plane is relatively more posterior than the mandibular terminal plane In the distal step relationship, the maxillary terminal plane is relatively more anterior than the mandibular terminal plane Determining the terminal plane relationships in the primary dentition stage is of great importance to the clinician because the erupting permanent 1 st molars are guided by the distal surfaces of the 2 nd primary molars as they erupt into occlusion

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Primary Teeth Resorption It was thought that primary tooth resorption is associated with eruption of permanent successors Primary teeth may resorb even in the absence of permanent teeth Inflammation and occlusal trauma hasten the tooth resorption Delayed by splinting Delayed if permanent successors absent

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Mixed Dentition Stage Starts with the eruption of the 1 st permanent tooth, usually the mandibular central incisor and is normally completed at the time the last primary tooth is shed

MESIAL DRIFTING TENDENCY There is strong tendency of teeth to drift mesially even before they erupt. This phenomenon is termed as MESIAL DRIFTING TENDENCY. :

MESIAL DRIFTING TENDENCY There is strong tendency of teeth to drift mesially even before they erupt. This phenomenon is termed as MESIAL DRIFTING TENDENCY.

Dental Arches and Dimensional Changes Maxillary alveolar diverge while the mandibular alveolar processes are more parallel Intercanine distance increases only slightly in the mandible as a result of distal tipping of primary cuspids into the primate spaces. In contrast, maxillary canines are placed distally pointing mesially and labially, hence their arrival is imp. In widening max. arches Mandibular arches perimeter dimineshes due to Late mesial shift of 1st molars into leeway space Mesial drifting tendency Slight amount of inter-proximal wear Lingual position of the incisors as a result of diff. M-M growth Original tipped positions of the incisors and molars Maxillary circumference only increases slightly:

Dental Arches and Dimensional Changes Maxillary alveolar diverge while the mandibular alveolar processes are more parallel Intercanine distance increases only slightly in the mandible as a result of distal tipping of primary cuspids into the primate spaces. In contrast, maxillary canines are placed distally pointing mesially and labially, hence their arrival is imp. In widening max. arches Mandibular arches perimeter dimineshes due to Late mesial shift of 1 st molars into leeway space Mesial drifting tendency Slight amount of inter-proximal wear Lingual position of the incisors as a result of diff. M-M growth Original tipped positions of the incisors and molars Maxillary circumference only increases slightly

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Nolla Stages of Development Nolla divided the development of each tooth into ten stages 0 Absence of crypt 1 Presence of crypt 2 Initial Calcification 3 1/3 rd crown completed 4 2/3 rd crown completed 5 Crown almost completed 6 Crown completed 7 1/3 rd root completed 8 2/3 rd root completed 9 Root almost completed (open apex) 10 Apical end of root completed

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Clinical implication Dental Age Delayed Eruption Accelerated Eruption Apexogenesis and tooth morphogenesis Space Management

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Dental Age Characteristics of various dental ages are defined as Dental age 6 Eruption of Dental age 7 Eruption of 6 6 6 1 1 6 1 1 2 2

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Dental age 8 Eruption of Dental age 9 1/3 rd root formation Crown almost completed root formation just started 2 2 4 4 4 3 3 4 753 357 5 5

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Dental age 10 1/2 root formation 1/3 rd root formation Note No teeth erupt in dental age 9 & 10 4 4 4 3 3 4 753 357 5 5

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Dental age 11 Eruption of 1/2 root formation Dental age 12 Eruption of 4 4 4 3 3 4 753 357 5 5 753 357 5 5

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Sequence of Eruption Maxilla 6124357 Mandible 6123457

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This child reported with exfoliated upper & lower right “c” though permanent cuspids have not yet erupted. “c`s” of left side are seen in the oral cavity. History showed that UR “c” was not extracted to allow the eruption of UR 2 rather normal physiological eruption of UR 2 lead to earlier exfoliation of UR “c” and slight midline shift.

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UR “3” & LR “5” have erupted slightly earlier. Ideally they should be erupted at 12 yrs of age along with 7`s. It is important to extract UL “c”& LL “e” immediately so that the successors can erupt thereby preventing malocclusion to occur.

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Dental age corresponds to the Chronological age of the child though UR “b” is still there in the oral cavity while UL 2 has just made its appearance.

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LR 12 and LL 12 are congenitally missing .Lower a`s and b`s are retained though roots are almost resorbed with grade 2 mobility. LL 5 is also congenitally missing

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Ideal 8 yr depiction

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Upper incisors are of abnormal shape and dimension. There is difference in the mesio-distal dimension of lower erupting right 3.

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This child has earlier eruption of lower 3`s & UR 4 .Moreover earlier exfoliation of upper C`s .UL “d” is still present . It is also important to mention that there is no space for upper cuspids to erupt in the oral cavity. Clinical examination conforms there eruption on the buccal sides.

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Upper 1`s have not yet appeared while the upper 2`s have made their appearance in the oral cavity. There is delayed eruption of Upper 1`s. Patient`s gives history of trauma to upper a`s which might have lead to this problem. Again some dentist have extracted the upper right d rather conserving it with endodontic means.

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Child has earlier eruptions of LR 4, 5 & LL 4. Moreover LR c & UR c have earlier exfoliations

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Delayed Eruption Early loss of deciduous teeth leads to formation of fibrous tissue on the eruption site, hence delays the eruption

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Accelerated Eruption Loss of deciduous teeth or extraction of deciduous tooth at Nolla stage 7or 8 of permanent teeth, accelerates the eruption of permanent teeth. Apexogensis and tooth movement At age 8, apex of incisors is not closed so teeth can be moved orthodontically mesiodistally but not labiolingually

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There are two important aspects to be considered in the mixed dentition 1) Utilization of arch perimeter 2) Adaptive changes in occlusion

Utilization of Arch Perimeter Accommodation of permanent incisors Space for the cuspids and premolars Adjustment of molar occlusion:

Utilization of Arch Perimeter Accommodation of permanent incisors Space for the cuspids and premolars Adjustment of molar occlusion

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Incisor Liability Inter-dental incisor spacing in the primary dentition Arch width increase Greater Labial inclination of permanent teeth Increase in primary inter-canine width Note Combined mesio-distal width of permanent incisors is 7.6 mm greater in the maxillary arch and 6 mm greater in mandibular arch

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Clinical Implication Maxillary Diastema Mandibular Crowdingf of 1-2 mm at age 8-9 yrs

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Leeway Space Combined mesio-distal width of c d e is larger than combined mesio-distal width of 3 4 5. This extra space is called as Leeway space Leeway space in upper arch is 0.9 mm / quadrant Leeway space in lower arch is 1.7 mm / quadrant Note This extra amount space is utilized for achieving Class I molar relation from the flush terminal plane. (Though other factors also are important)

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E Space Mesio-distal width of E is more than the 5

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Clinical Significance If combined mesio-distal width of unerupted 3 4 5 is equal to or greater than c d e than the condition is termed as Leeway space discrepancy and crowding often results Space management is required

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Occlusal Changes in the mixed dentition The usual flush terminal of primary dentition provides an end to end relationship of 1 st permanent molars. The 1 st permanent molar normally achieve Class I by Late mesial shift after the loss of e`s Greater forward growth of mandible than maxilla Combination of 1 & 2

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Clinical Significance Distal step in primary dentition needs earlier correction as otherwise child may develop Class II or end to end M/R Mesial step > 2mm in primary dentition earlier needs correction as otherwise child develops Class III M/R

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Permanent Dentition stage Strats after the shedding of the last primary tooth and eruption of all permanent teeth excluding 3 rd molars

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Late Changes in the permanent dentition stage Changes do occur but at a slower rate 1) Inter-incisor width decreases with age 2) Inter-canine width decreases with age 3) Lips become more retruded with age relative to the nose and chin so orthodontic treatment should not result in an overlay straight or retrusive profile (Am J Orthod sept. 2003 )

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Characteristics of Permanent Dentition Class I relationship (molar, premolar, canine & incisors) Angulations Inclinations No rotations Tight proximal contacts Arch curvatures

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ANTERIOR COMPONENT OF FORCE The tooth`s position is affected by the lips, cheeks and tongue muscles etc. All these factors along with axial inclination of permanent teeth produce a resultant force through the contact points of the teeth, known as ANTERIOR COMPONENT OF FORCE. The anterior component of force is countered by the approximal contacts of teeth and by musculature of the lips and cheeks

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