Head and Neck embryology

Tooth Development Review head and neckblk embryology Initiation to eruption

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Initiation Initiation

stomodeum Epithelial cells (dental lamina) During 6th week, ectoderm in stomodeum forms horseshoe shaped mass of oral epithelium mesenchyme Basement membrane mesenchyme

Initiation of anterior primary teeth Epithelial cells in horseshoe Dental lamina begins begins the sixth to seventh week form dental lamina growing into mesenchyme of development, initiation of additional At site where tooth will be teeth follows and continues for years

Dental Lamina – Initiation

Supernumerary tooth

PREDICT what would happen if an extra tooth was initiated. Mesiodens

1 Bud Stage – eighth week Bud Stage

Epithelium (dental Lamina) Dental lamina grows down into mesenchyme at site of tooth.

Mesenchyme starts to change composition in response

mesenchyme

PREDICT what would happen if two tooth buds fused together or one tooth bud split in half.

Fusion/Gemination Cap stage – week 9

By week 9, all germ layers of future tooth have formed

ElEnamel organ ( enamel ll) only)

Dental papilla (dentin and pulp)

Fusion Gemination Dental sac (cementum, PDL, Alveolar bone)

PREDICT how you would know if it was mesenchyme fusion or gemination

Cap Stage Successional Dental Lamina

Each primary tooth germ has epithelium a successional lamina that becomes a permanent tooth Succedaneous teeth replace a deciduous tooth, nonsuccedaneous do not

IDENTIFY nonsuccedaneous teeth

mesenchyme PREDICT What occurs if no successional lamina forms?

2 Congenitally missing teeth Bell Stage – Enamel Organ

Outer enamel epithelium (OEE) Protective coating Inner enamel epithelium (IEE) Will become ameloblasts No succedaneous tooth Stratum Intermedium helps make enamel

What tooth is missing? Identify tooth C Stellate reticulum Basement membrane Supports enamel formation

Bell Stage Bell Stage – Dental Papilla

Outer cells of papilla Will become odontoblasts

Inner cells of papilla will become pulp

Formation of enamel and dentin Formation of enamel and dentin Inner enamel epithelium basement membrane When nuclei of IEE move away from Outer cells of papilla basement membrane, they become preameloblasts NliNuclei Nuclei of outer cells of papilla then move away from basement membrane and become odontoblasts. The odontoblasts then begin laying down dentin matrix.

3 Dentin formation Types of dentin

Odontoblast starts here (at what once was • Peritubular dentin - basement membrane) Highly mineralized And ends up in pulp chamber dentin surrounding tublbule As it moves and lays down dentinal matrix, it leaves part of itself behind so it ends up • Intertubular dentin- looking like this dentin between tubules Odontoblastic process • Mantle dentin- first dentin to be laid down Body of cell

PREDICT why exposed dentin is sensitive

Dentin Formation Dentin Formation

• The dentin that is present when a tooth erupts is called “primary dentin”. Dentinal tubule (occupied by odontoblastic • Odontoblasts continue to produce dentin after process) eruption making pulp chamber smaller . This is “secondary dentin”. Peritubular dentin (highly mineralized) • Odontoblasts also make “reparative dentin” in response to trauma. It has no tubules. Intertubular dentin • Dead odontoblasts make empty tubules called (bulk of dentin) “dead tracts”.

Calcified dentin cross section

Types of dentin • Tertiary (reparative) dentin • Laid down in response to trauma

•A –Enamel • B – Primary dentin • C – Secondary dentin • D – Mantle dentin • E – Circumpulpal dentin

4 Dentinogenesis Imperfecta Pulp Abnormality

• Autosomal dominant defect “Pulp stone” is calcified mass in pulp

• Enamel chips off Few are true “denticles” because it is produced by odontoblasts. unsupported Most are layers of calcium • Teeth have bluish surrounding dead cells color

Formation of enamel Formation of Enamel

Millions of ameloblasts They end up here, each After odontoblasts lay down predentin, starts here at what was leaving enamel matrix basement membrane disintegrates and basement membrane behind preameloblasts become ameloblasts

Tome’s Dentin and enamel process Ameloblasts then begin moving away matrix later replaced From what was basement membrane with hydroxyapatite secreting enamel matrix from Tome’s crystals of calcium, process phosphorus and fluoride (if available)

Enamel Cuticle and Reduced Enamel Epithelium Enamel Rods • Last thing ameloblasts do is produce primary enamel cuticle which Key shaped enamel matrix (enamelon) coats tooth is replaced with hydroxyapatite crystals oflif calcium, ph osph orus and dflid(if fluoride (if • IEE then joins with available) to form an enamel rod OEE to form reduced enamel epithelium Enamel matrix not laid down evenly so calcification varies. Variations seen as (REE) Stria of Retzius and incremental lines

5 Eruption Attachment apparatus

• REE joins with oral • As tooth erupts, REE epithelium becomes part of • REE then produces attachment apparatus enzymes that dissolve epithelium, creating eruption tunnel • Enzymes cause inflammation which causes “teething” pain

Enamel Abnormalities -Amelogenesis Imperfecta Enamel Abnormalities - Hypocalcification

• Genetic defect • Appear as white spots • Imperfect enamel • The spots can be as matrix or hard as normal tooth hypocalcification or hyypomaturation

Enamel Abnormalities – Turner’s tooth Enamel Abnormalities – high temperature

• Enamel hypoplasia • Enamel hypolasia caused by injury to caused by high fever succedaneous tooth during illness • At what age was the fever

6 Enamel Abnormalities – Fluorosis Root Formation

• In large amounts, fluoride can cause staining or pitting Root formation begins (lhli)(enamel hypoplasia) At the “ cervi cal l oop” Enamel organ IEE and OEE join (bell stage) together to make Hertwig’s root sheath

Root formation begins after enamel matrix is laid down but before calcification

Cervical loop and Hertwig’s root sheath

Outer enamel epithelium (OEE) Inner enamel epithelium (IEE)

Cervical loop grows down into mesenchyme to form Cervical loop Hertwig’s rooth sheath. Number of roots is determined by the way it Epithelial diaphragm grows.

Root Formation Cementum Formation

60% of the time, cementum overlays enamel As root sheath 30% of th e ti me cement um meet s enamel grows, it stimulates Enamel dental papilla The odontoblasts cause the papilla cells to become sheath to dissolve 10% of the time cementum does not meet dentin odontoblasts enamel exposing dentin and form dentin When the odontoblasts Cementum contact the dental sac, PREDICT what a patient might experience when they create cementoblasts dental sac cementum does not meet enamel that start making cementum

7 Cementum Formation Root abnormalities - Concrescence

• A form of fusion • In cervical 2/3 of tooth, cementoblasts dissolve, so • Teeth joined by its acellular cementum cementum • In the apical 1/3, cementoblasts get trapped in developing cementum as cementocytes, can later lay down more cementum

Dilaceration Enamel pearl

• Abnormal shape of • Hertwig root sheath root cells differentiate into • Problem for dentist ameloblasts during extraction • Can be confused with calculus

Supernumerary roots Taurodontism

• Most often seen in • Also called “bulls third molars teeth” • Extra large pulp chamber • No constriction at CEJ • Genetic link

8 Lateral abnormalities Talon Cusp

• On axillary laterals and central incisors • Cusp contains pulp horn

Microdontia Dens in dente

CYSTS Dentigerous Cyst Odontogenic cysts arise from the enamel organ or remnants of Hertwigs’s rooth sheath. • Also called follicular cyst • Associated with unerupted tooth • Arises from reduced enamel epithelium • Most common in mandible Radicular (periapical) Radicular cyst cyst clinically

Dentigerous cyst Odontogenic Keratocyst

• Can lead to • Arises from enamel ameloblastoma organ, contains keratin • Frequently reoccurs! • Multilocular • Grows aggressively

9 Primordial cyst Residual cyst

• Cyst develops instead • A radicular cyst that of tooth, was not enucleated • Most common in third when tooth removed molar region • Differentiate from a • Always associated primordial cyst with a missing tooth • Can become ameloblastoma

Eruption cyst Lateral periodontal cyst

• Fluid trapped between • Arises from Hertwig’s tooth and reduced root sheath enamel epithelium • Found in bone • Resolves when tooth • Most often near erupts mandibular cuspid or premolar

Gingival cyst Eruption Rules

• Found in soft tissue • Teeth of girls erupt sooner than boys • Same as lateral • Permanent teeth start forming 6 years before periodontal cyst eruption, deciduous 2.5 years • Mandibular teeth erupt before maxillary • Roots not completely formed when tooth erupts • The permanent crown is completely formed 3 years before it erupts

PREDICT why cohort girls have a higher DMF than boys

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