Development of dentition and occlusion Dr. Zuber Ahamed Naqvi

OBJECTIVES Stages of tooth development Pre – dental period The deciduous dentition period The mixed dentition period The permanent dentition period

Stages of tooth development (based on shape of enamel organ): Bud stage Cap stage Bell stage

Tooth formation Primary epithelial bands: Horseshoe-shaped bands. Two subdivisions: vestibular lamina and dental lamina vestibule dental arches BUD STAGE Tooth bud Oral epithelium Mesenchyme

Cap Stage Histodifferentiation (differentiation of tissues) Morph differentiation Dental papilla dentin and pulp tissue (mesenchymal origin) Basement membrane separating the dental organ and the dental papilla becomes the future site for the dentinoenamel junction (DEJ) Remaining mesenchyme surrounds the dental/enamel organ and condenses to form the dental sac or the dental follicle

Bell Stage Early bell stage Advanced bell stage Bell-like shape differentiation produces four types of cells within the enamel/dental organ 1. inner enamel epithelium 2. outer enamel epithelium 3. stellate reticulum 4. stratum intermedium The dental papilla undergoes differentiation and produces two types of cells 1. outer cells of the DP – forms the dentin-secreting cells (odontoblasts) 2. central cells of the DP – forms the primordium of the pulp

ROOT FORMATION Takes place as the crown is completely shaped and the tooth begins to erupt Root formation is through the formation of a cervical loop (CL) Two layers consisting of Iner enamel epithelium and outer enamel epithelium The CL begins to grow down into the dental sac It forms a Hertwig's root sheath

Periodontal ligament The mesenchyme of the dental sac condenses to form the periodontal ligament The cells of the disintegrating Hertwig root sheath develop into discrete islands of epithelial cells become epithelial rests of Malassez

Development of occlusion Occlusion is the relationship of the mandibular and maxillary teeth when closed or during excursive movements of the mandible; when the teeth of the mandibular arch come into contact with the teeth of the maxillary arch in any functional relationship.

Periods of occlusal development 1. Pre – dental period 2. The deciduous dentition period 3. The mixed dentition period 4. The permanent dentition

GUM PADS • The alveolar processes at the time of birth are known as gum pads The gum pads are pink, firm & covered by a dense layer of fibrous periosteum They are HORSE-SHOE shaped & develop in two parts: the labio-buccal portion & the lingual portion • The two portions of the gum pads are separated from each other by a groove called the dental groove dental groove

GUM PADS Lateral sulcus-The transverse groove b/w canine & first deciduous molar segment . The lateral sulcus of the mandibular arch is normally more DISTAL to that of the maxillary arch The gum pads are divided into TEN SEGMENTS by certain grooves called TRANSVERSE GROOVES • Each of these segments consist of one developing deciduous tooth sac • The gingival groove separates the gum pads from the palate & floor of the mouth

There is a complete overjet all around (1) Contact occurs b/w the upper & lower gum pads in the first molar region (2) A space exist b/w them in the anterior region • This infantile open bite is Open bite considered normal & it helps in suckling

Teeth that are present at the time of birth are called NATAL TEETH Neonatal teeth Teeth that are present at the time of birth are called NATAL TEETH Teeth that are erupt during the first month of age are called Neonatal teeth The natal & neonatal teeth are mostly located in the mandibular incisor region & Show a familial tendency.

The deciduous dentition period Primary teeth begin to erupt at the age of 6 months. The eruption of all primary teeth is completed by 2.5 to 3.5 years of age when second deciduous molars come into occlusion.

The mixed dentition period The mixed dentition period begins at approximately 6 years of age with the eruption of the first permanent molars. primary + permanent teeth (6 Y – 12 Y) Classified into three phases: 1. First transitional period 2. Inter-transitional period 3. Second transitional period

First transitional period The first transitional period is characterized by : the emergence of the first permanent molars & (2) the exchange of the deciduous incisors with the permanent incisors The mesio-distal relation b/w the Distal Surfaces of the upper & lower second deciduous molars can be of three types : FLUSH PLANE MESIAL STEP DISTAL STEP

Flush to Class I molar relation This occurs by- utilization of the physiological spaces and primate spaces( early shift) & leeway space in the lower arch ( late shift) (3) by differential forward growth of the mandible

Inter – transitional period • In this period the maxillary & mandibular arches consist of Sets of deciduous & permanent teeth 6edc21

Second transitional period • Leeway space of Nance - The combined mesio-distal width of the permanent canines & premolars is usually less than that of the deciduous canines & molars Maxillary arch - 1.8mm (0.9 mm in each quadrant of the arch) Mandibular arch- 3.4mm (1.7 mm in each quadrant of the arch) The normal leeway space according to Moyers is 2.6 mm in the maxilla and 6.2 mm in the mandible.

The ugly duckling stage: • As the developing permanent canines erupt, they displace the roots of the lateral incisors mesially. • This result in transmitting of the force on to the roots of the central incisors which also get displaced mesially • A resultant distal divergence of the crowns of the two central incisors causes a midline spacing • This situation has been described by Broadbent as the ugly duckling stage.

The permanent dentition period The eruption sequence of the permanent dentition may exhibit variation • The frequently seen sequences in the maxillary arch are: – 6 – 1 – 2 – 4 – 5 – 3 – 7 or – 6–1–2––4 -3–5–7 In case of the mandibular arch the sequence is – 6 – 1 – 2 – 3 – 4 – 5 – 7 or – 6–1–2–4–3–5–7

References: Contemporary orthodontics. 5th edition. William R Proffit Orthodontics : the art and science. 4th edition. S I Bhalaji Dentistry for the child and adolescent. 8th edition. Ralph E. McDonald, David R. Avery, Jeffrey A. Dean