Development of dentition from birth to complete deciduous dentition

• Soon become segmented and each segment is a developing tooth site 
• Pink in color 
• Firm in consistency 
• Get divided into a labio/buccal and a lingual portion which differentiates later 
• Transverse grooves separate the gum pads into 10 segments
• The groove between the canine and the first molar region is called the lateral sulcus, which helps to judge the inter-arch relationship

The upper gum pad is horse shoe shaped and shows

• Gingival groove: Separates gum pad from the palate
• Dental groove: Starts at the incisive papilla, extends backward to touch the gingival groove in the canine region and then moves laterally to end in the molar region
• Lateral sulcus

The lower gum pad is U-shaped and rectangular characterized by 

• Gingival groove : Lingual extension of the gum pads
• Dental groove : Joins gingival groove in the canine region
• Lateral sulcus

Relationships of gum pads

• Anterior open bite is seen at rest with contact only in the molar region. Tongue protrudes anteriorly through this space. The intermaxillary space closure, occurs with eruption of primary teeth, thus it is a self-correcting anomaly of the developing dentition
• Complete overjet
• Class II pattern with the maxillary gum pad being more prominent
• Mandibular lateral sulci posterior to maxillary lateral sulci
• Mandibular functional movements are mainly vertical and to a little extent anteroposterior. Lateral movements are absent

Neonatal jaw relationship

• No precise “bite” or jaw relationship yet
• Cannot be used as a diagnostic criterion for reliable prediction of subsequent occlusion in the primary dentition

Precociously erupted primary teeth

• Occasionally a child is born with teeth already present in the mouth (natal tooth)
• These teeth are almost always mandibular incisors, which frequently display enamel hypoplasia
• They should not be removed if normal but removed if supernumerary or mobile

Jaw development 

• At birth, both maxilla and mandible are small compared to the rest of the face
• Overjet diminishes markedly during the first 6 months
• Increase in jaw size provides enough space for harmonious arrangement of deciduous teeth
• Crowding seen in the pads disappears when the teeth erupt
• Eruption of deciduous teeth commences at about 6 months of age
• Occlusion starts developing posteriorly when deciduous first molars attain contact
• By the time the first molars have settled, occlusion in the posterior region is established

• Starts from eruption of the first deciduous tooth, usually the deciduous mandibular central incisors
• Ends with the eruption of the first permanent molar
• By 2½ years of age, deciduous dentition is usually complete and in full function
• Root formation of all deciduous teeth is complete by 3 years of age

Normal signs of primary dentition

• Spaced anteriors : to accommodate larger permanent teeth in the jaws
• Primate / simian / anthropoid space : present mesial to the maxillary canine and distal to the mandibular canine. This space is used for early mesial shift
• Shallow overjet and overbite
• Almost vertical inclinication of the anteriors
• Ovoid arch form
• Straight / flush terminal plane relation : based on distal surface of mandibular second molar 

Flush terminal plane : When the distal surfaces of maxillary and mandibular deciduous second molars are in the same vertical plane; this is the normal molar relationship in the primary dentition because the mesiodistal width of the mandibular molar is greater than the mesiodistal width of the maxillary molar

Mesial step : Distal surface of mandibular deciduous second molar is mesial to the distal surface of maxillary deciduous second molar

Distal step : Distal surface of mandibular deciduous second molar is more distal than the distal surface of maxillary deciduous second molar, i.e. the upper second molar occludes with two opposite teeth

• Period where teeth of both deciduous and permanent dentition are seen
• Extends from 6-12 years of age
• Can be divided into two transitional periods : first and second

First transitional period

1. Eruption of permanent first molars : First permanent molars erupt at 6 years

Anteroposterior positioning of permanent molars is influenced by 

1. Terminal plane relationship 

• When the deciduous second molars are in a flush terminal plane, the permanent first molar erupts initially into a cusp-to-cusp relationship, which later transforms into a Class I molar relation using primate space and later mesial shift of permanent first molar following exfoliation of the primary molar and thus making use of Leeway space 
• When the deciduous second molars are in a distal step, the permanent first molar will erupt into a Class II relation. This is not self-correcting and will cause a Class II malocclusion despite Leeway space and differential growth
• Primary second molars in mesial step relationship lead to a Class I molar relation in mixed dentition. This may remain or progress to a half or full cusp Class III with continued mandibular growth

2. Early mesial shift in arch with physiologic spacing 

• In a spaced arch, eruptive force of the permanent molars causes closing of any spaces between the primary molars or primate spaces thus allowing molars to shift mesially 

3. Differential growth of maxilla and mandible 

4. Eruption of incisors

• Permanent incisors develop lingual to the primary incisors
• For incisors to erupt in normal alignment, there is an obligate space requirement in the anterior part of both the arches which is termed as incisor liability

Obligate space is provided by

• Interdental physiologic spacing in the primary incisor region: 4 mm in maxillary arch; 3 mm in mandibular arch
• Increase in the inter-canine arch width: Significant amount of growth occurs with the eruption of incisors and canines
• Increase in the anterior length of the dental arches: Permanent incisors erupt labial to the primary incisors to obtain an added space of 2-3 mm
• Change in inclination of permanent incisors: Primary teeth are upright but permanent teeth incline to the labial surface thus decreasing the inter-incisal angle from about 150° in the deciduous dentition to 123° in the permanent dentition. This increases the arch perimeter

The broadbent’s phenomenon : ugly duckling stage

• Around the age of 8 years, a midline diastema is commonly seen in the upper arch
• Crowns of canines in young jaws impinge on developing lateral incisor roots, thus driving the roots medially and causing the crowns to flare laterally
• The roots of the central incisors are also forced together thus causing a maxillary midline diastema
• Unaesthetic metamorphosis, which eventually leads to an aesthetic result
• With eruption of canines, the impingement from the roots shifts incisally thus driving the incisor crowns medially, resulting in closure of the diastema

• Stable phase where little changes take place in the dentition
• Teeth present : permanent incisors, first molar + deciduous canines and molars
• Any asymmetry in emergence and corresponding differences in height levels or crown lengths between the right and left side teeth are made up
• Occlusal and interproximal wear of deciduous teeth causes occlusal morphology to approach that of a plane
• Ugly duckling stage
• Root formation of emerged incisors, canines and molars continues, along with concomitant increase in alveolar process height
• Resorption of roots of deciduous molars

• At around 10 years of age, the first deciduous tooth in the posterior region, usually the mandibular canine sheds and marks the beginning of the second transitional period
• Usually no crowding is seen before emergence except maybe between the maxillary first premolar and canine

Eruption of permanent canines and premolars

• Erupt after a pause of 1-2 years following incisor eruption
• The first posterior teeth to erupt are the mandibular canine and first premolar (9-10 years) followed by maxillary premolars and canine around 11-12 years
• Most common eruption sequence : 4-5-3 in maxilla, 3-4-5 in mandile
• Favorable occlusion in this region is largely dependent on: Favorable eruption sequence, Satisfactory tooth size- available space ratio, Attainment of normal molar relation with minimum diminution of space available for bicuspids

Eruption of permanent second molars 

• These teeth are formed palatally and are guided into occlusion by the Cone Funnel mechanism
• The arch length is reduced prior to second molar eruption by the mesial eruptive forces
• Therefore, crowding if present is accentuated

Establishment of occlusion

• Calcification begins at birth with the calcification of the cusps of the first permanent molar and extends as late as the 25th year of life
• Complete calcification of incisor crowns takes place by 4 to 5 years and of the other permanent teeth by 6 to 8 years except for the third molars

Features of the permanent dentition

• Coinciding midline
• Class I molar relationship of the permanent first molar
• Vertical overbite of about one-third the clinical crown height of the mandibular central incisors
• Overjet: Overjet and over bite decreases throughout the second decade of life due to greater forward growth of the mandible
• Curve of Spee: Develops during transition and stabilizes in adulthood

• Eruption of mandibular central incisor and permanent first molar
• Mandibular molar eruption precedes maxillary molar

• Eruption of maxillary central and mandibular lateral incisor
• Root formation of maxillary lateral incisor well advanced
• Crown completion of canines and premolars

• Eruption of maxillary lateral incisor
• Delay of 2-3 years before any further teeth erupt

• One-third root formation of mandibular canine and first premolar is complete
• Root development of mandibular second premolar begins

• One-half root formation of mandibular canine and first premolar is complete
• Significant root development of maxillary and mandibular second premolar as well as maxillary canine
• Root completion of mandibular incisors and near completion of maxillary lateral
• According to Moyers, mandibular canine erupts between 9 and 10 years

• Eruption of mandibular canine (according to Proffit), mandibular first premolar and maxillary first premolar
• Maxillary first premolar erupts ahead of canine and second premolar

• Remaining succedaneous teeth erupt
• Second permanent molars nearing eruption
• Early beginnings of third molar

• Completion of roots of permanent teeth
• Third molars apparent on the radiograph
• Eruption of second molars ahead of premolars in the mandibular arch. This decreases the space for second premolars, which get partially blocked out
• Eruption of maxillary canines ahead of premolars will cause the canines to be forced out labially
• Asymmetries in eruption between the right and left sides occurs when there is lack of space to accommodate erupting teeth due to different pattern of mechanical obstruction, decreased space on one side compared to the other