Development of the Dentition

Development of the Dentition

• Teeth develop from the dental lamina, first evidence of formation is at 6-7 weeks in utero.
• Tooth development is divided into bud, cap and bell stages.
• Dental age does not correlate well with chronological age.
• Knowledge of the normal eruption sequence is crucial for detecting eruption disturbances.

Stages of Dentition

• Primary Dentition (6 months to 6 years): This is the period where deciduous teeth erupt and are fully functional. Stages include early erupted period and stable period.
• Mixed Dentition (6 years to 12 years): Both primary and permanent teeth are present in the mouth. Stages include first transitional period, a stable period (8-10 years), and second transitional period.
• Permanent Dentition (over 12 years): Only permanent teeth are present; characterized by the late eruption of the third molars. Stages include stable period and late erupted period.

The Primary Dentition

• The timing of calcification, eruption, and root completion of the primary dentition is outlined in a table.
• Includes eruption sequence and calcification beginning (in utero) for various primary teeth.

Signs of Primary Dentition

• Spacing between upper incisors: Normal spacing between upper incisors is typical
• Mild spacing between lower incisors: Normal mild spacing in between lower incisors is typical
• Primate spaces: Spacing is noticeable distally to the maxillary lateral incisors and mandibular canines.
• Almost vertical inclination of anteriors: Normal almost vertical inclination of the anterior teeth
• Shallow overjet and overbite: Normal shallow overjet and overbite is characteristic of the primary dentition
• Flat Occlusal Plane: Normal flat occlusal plane is characteristic of the primary dentition
• Straight Terminal plane: Normal straight terminal plane relation is typical

Second Deciduous Molar Relationship

• Second deciduous molar relationship includes three types
• Distal step (10%)
• Flush terminal plane (30%)
• Mesial step (60%)

The Mixed Dentition Stage

• Transition from primary to permanent dentition begins around age 6.
• Eruption of the first permanent molars marks the start of this stage, followed shortly by the permanent incisors.

Dental Ages and Characteristics

• Dental age 8: Maxillary lateral incisors begin erupting.
• Dental age 9: Maxillary lateral incisors have been in place for a year; root formation is nearly complete for other incisors/molars; root development of canines and premolars is still beginning.
• Dental age 11: Simultaneous eruption of mandibular canines, mandibular first premolars and maxillary first premolars is typical.
• Dental age 12: Eruption of remaining succedaneous teeth is occurring (typically, the maxillary canine, and the maxillary and mandibular second premolars) followed a few months later by the maxillary and mandibular second molars.
• Dental age 15: Roots of all permanent teeth, except for the third molars, are typically complete; crown formation of the third molars is often complete.

Eruption of Permanent Teeth (Table)

• A table displays the eruption sequence & the approximate timing of calcification for different permanent teeth.

Replacement of Central and Lateral Incisors

• The total mesiodistal width of four permanent incisors is greater than the width of four primary incisors.
• The difference, called obligate space, is approximately 7.5 mm in the maxilla and 5.5 mm in the mandible.
• The lack of obligate space is resolved by physiological spacing between incisors and natural growth of the inter-canine arch width.

Replacement of Canine, First, and Second Premolars

• The combined mesiodistal width of deciduous canine with first and second molars is greater than the permanent canine with first and second premolars.
• The difference, known as leeway space, is larger in the lower arch (2.5 mm per side) compared to the upper arch (1.5 mm per side), due to the larger size of the lower second deciduous molars.

Surplus of Leeway Space

• The surplus leeway space is used to transform molar cusp-to-cusp relations into cusp-to-groove relations (class I molars).
• It's also used for resolving moderate crowding.

Evolution of Molars Relationship

• First permanent molars erupt at 6 years and play a key role in occlusion.
• Anteroposterior positioning of permanent molars is influenced by:
• Initial terminal plane relationship of second primary molars
• Differential growth of the mandible and maxilla
• Positive mesial shift degree, given by leeway space

Molar Relationships (diagram)

• Shows the different relationships of primary and permanent molars (Class I, II, III) with reference to various growth patterns.

The Broadbent's Phenomenon (Ugly Duckling Stage)

• Around age 8, the canine crowns begin impinging on the roots of the lateral incisors, causing distal flaring of the incisor crowns.
• Continued canine eruption causes the closure of the diastema.

Signs of Mixed Dentition

• Distal flaring of upper incisors
• Minor crowding of lower incisors
• Positive leeway space in lateral sectors
• Modest labial inclination of anteriors
• Edge-to-edge molar relationships
• Moderate curve of Spee