DEVELOPMENT OF TEETH and ASSOCIATED STRUCTURES By Dr

DEVELOPMENT OF TEETH, and ASSOCIATED STRUCTURES By: Dr. Richa Khanna Asst Prof. Paediatric and Preventive Dentistry, KGMU, Llko.

Specific Learning Objectives You should be able to: 1. Enumerate different stages of tooth development 2. Describe characteristics features of each stage. 3. Describe vascular and nerve supply during tooth development 4. Describe stages of enamel formation. 5. Describe root formation during tooth development

Development of dentition starts as early as the sixth week of prenatal life… …and is divided into the following stages

PRENATAL STAGE Oral arise epithelium in both jaws points thickens, Local buds at twenty different on forming the labial side Duration: 6 th arise weeks to 9 onmonths in utero At 16 weeks small buds also the lingual side. These dental lamina of dental lamina, representing the primordia of the are the early anlage of the permanent teeth. deciduous teeth

The individual tooth formation consists of following stages: 1. Bud Stage 2. Cap Stage 3. Bell Stage

Bud Stage The bud stage is characterized by the appearance of a tooth bud without a clear arrangement of cells. It is characterized by rounded, localized growth of epithelium surrounded by proliferating mesenchymal cells.

Bud Stage In the bud stage, the enamel organ consists of peripherally located low columnar cells and centrally located polygonal cells

Cap Stage • First signs of an arrangement of cells in the tooth bud occur in the cap stage. • The tooth bud grows around the ectomesenchymal aggregation, taking on the appearance of a cap, and becomes the enamel (or dental) organ.

Enamel organ Dental follicle Dental papilla • A small group of ectomesenchymal cells stops producing extracellular substances, resulting in an aggregation of these cells called the dental papilla. • A condensation of ectomesenchymal cells called the dental follicle surrounds the enamel organ and limits the dental papilla • Eventually, the enamel organ will produce enamel, the dental papilla will produce dentin and pulp, and the dental follicle will produce all the supporting structures of a tooth

Bell Stage stellate reticulum outer enamel epithelium • Histodifferentiation and morphodifferentiation takes place • Dental organ is bell-shaped during this stage, and the majority of its cells are called stellate reticulum because of their star-shaped appearance • Cuboidal cells on the periphery of the dental organ are known as outer enamel epithelium.

• The columnar cells of the enamel organ adjacent to the dental papilla are known as inner enamel epithelium. • The cells between the inner enamel epithelium and the stellate reticulum form a layer known as the stratum intermedium. inner enamel epithelium outer enamel epithelium

§ The rim of the dental organ where the outer and inner enamel epithelium join is called the cervical loop § The dental lamina disintegrates, leaving the developing teeth completely separated from the epithelium of the oral cavity. § Sometimes, these epithelial cells will persist and are called “epithelial pearls”or “cell rests of Serre” § Clinical significance: Cysts will develop in these (eruption cysts) and prevent eruption, or they may form odontomas(tumors) or may form supernumery teeth.

Enamel Knot: Densely packed accumulation of cells projecting from the inner enamel epithelium into enamel organ. Exact role not known, but currently believed to be the organizational center for cusp development

Enamel niche : It is an artifact produced during sectioning of the tissue. It occurs because the enamel organ is a sheet of proliferating cells rather than a single strand contains a concavity filled with ectomesenchyme

Crown pattern determination …. Occurs in Bell stage

Vascular and Nerve Supply during Tooth Development Vascular Supply: • Clusters of blood vessels in dental follicle and papilla. • Clustering of vessels in papilla coincide with position of root formation • Enamel organ is avascular, however vessels seen in close association in the follicle Nerve Supply: • Initially noted in the dental follicle during bud to cap stage • However after start of dentinogenesis, seen in dental papilla • Nerve fibers do not enter enamel organ

Deposition of dental hard tissues is called “apposition” Stages of Apposition 1. Elongation of inner dental epithelium • 2. Differentiation of odontoblasts from ectomesenchymal cells are induced by influence from the inner dental epithelium 3. Formation of dentin • First layer of dentin appears at the cusp tips and progresses cervically • As the organic matrix of dentin is deposited, the odontoblasts move towards the center of the dental papilla, leaving behind cytoplasmic extensions which will soon be surrounded by dentin. Therefore, a tubular structure of dentin is formed.

4. Formation of enamel • At the same time or soon after the first layer of dentin (mantle dentin) is formed, the inner dental epithelial cells differentiate into ameloblasts and secrete enamel proteins. • The boundary between the odontoblasts and inner dental epithelium defines the future dentinoenamel junction. • The formation of enamel is called amelogenesis.

Ameloblasts goes through following functional stages: 1. Morphogenetic. 2. Histodifferentiation 3. Secretory 4. Maturation 5. Protection:

Time Line of Human Tooth Development Age 42 to 48 days 55 to 56 days 14 weeks 18 weeks 32 weeks Developmental Characteristics Dental lamina formation Bud stage; deciduous incisors; canines and molars Bell stage for deciduous teeth; bud stage for permanent teeth Dentin and functional ameloblasts in deciduous teeth Dentin and functional ameloblasts in permanent first molars

ROOT FORMATION • Development of root begins after the enamel and dentin formation has reached the future cementoenamel junction • Epithelial cells of the inner and outer dental epithelium proliferate from the cervical loop of the enamel organ to form the Hertwig’sepithelial root sheath. • The root sheath determines if a tooth has single or multiple roots, is short or • long, or is curved or straight

ROOT FORMATION

FORMATIONOF PDL AND CEMENTUM • As the root sheath fragments, the dental follicle cells will penetrate between the epithelial cells and lie close to the newly formed root dentin. • These cells will differentiate into cementoblasts, which will make cementum • Fibers of the periodontal ligament, which will also form from the cells of the dental follicle will get anchored in the organic matrix of the cementum which will later get mineralized

Specific Learning Objectives You should be able to: 1. Enumerate different stages of tooth development 2. Describe characteristics features of each stage. 3. Describe vascular and nerve supply during tooth development 4. Describe stages of enamel formation. 5. Describe root formation during tooth development