ORSE - Embryology & Histology

What is Embryology?

The study of prenatal development; The stages before birth

What is Histology?

The study of structure and function of tissues on a microscopic level

How does pregnancy happen?

Conception; Fertilization of female ovum by male sperm

How many semesters are there in pregnancy and how many months each?

3 trimesters of 3 months each

When is the developmental age based on?

Based on the date of conception; 2 weeks after LMP

What is the organism called when a sperm and ovum unites?

Zygote

What are the 3 prenatal development periods?

1. Preimplantation

2. Embryonic

3. Fetal

When does the preimplantation period start?

First week

Why is the embryonic period the most critical time of development?

Embryo needs all the important nutrients; Period where things can go most wrong

When does the fetal period begin and end

9th week until birth

When does the face and related tissues form?

4th week within embryonic period

What is the stomodeum?

Primitive mouth

What are the 3 primary embryonic layers?

Ectoderm, Mesoderm, Endoderm

When do the embryonic layers form?

3rd week of development

When does the stomodeum and primitive pharynx merge?

4th week

What system develops from the endoderm?

Developing digestive system: Oropharyngeal membrane, pharynx, foregut

What develops from the ectoderm?

Enamel of teeth and lining of oral cavity; Developing brain and spinal cord

What develops from the mesoderm?

Dentin, pulp, cementum; Developing heart

At 5 weeks how long is the embryo?

5mm long

How many branchial arches have formed by the end of the 4th week

12 brachial arches; 6 pairs

What does the first branchial arch form?

Lower lip, muscles of mastication, anterior portion of mandibular alveolar process

What does the second branchial arch form?

Styloid process, stapes, stylohyoid ligament, part of hyoid bone

What do the other branchial arches form?

Body of hyoid, posterior tongue, structures of the lower throat

When does the formation of the palate start?

Beginning of the 5th week

What two embryonic structures is the palate formed by

Primary palate

Secondary palate

How are the hard and soft palates formed?

Union of primary and secondary palates

What shape does the fusion make and where?

Y-shaped pattern on the roof of the mouth

What is the formation order of the 3 stages?

1. Formation of the primary palate

2. Formation of the secondary palate

3. Fusion of palates

If there is a disruption what will happen to the palates?

Result in cleft lip or cleft palate

When doest the development of the human face occur?

Between 5th and 8th week of prenatal stage

What happens at 1 month?

Forehead is dominant feature

What happens at 4 months?

Face looks human, hard and soft palates begin to form, primary dentition begin

What happens during the last trimester?

Fat is laid down in cheeks

What is the fat in cheeks also known as?

Sucking pads

Where and when is the earliest signs of tooth development?

Anterior mandibular region; 5 to 6 weeks old (first trimester)

When does permanent teeth develop?

17th week

What are genetic factors?

During prenatal tooth development; tooth and jaw size

What are environmental factors?

Teratogens; infections, drugs, exposure to radiation

What is Tetracycline Stain?

When tetracycline is given to a pregnant mother during fetal period, systemic developmental staining (permanent endogenous) can occur; make teeth look gray

What are osteoblasts?

Cells that lay down or create new bone formation

What are Osteoclasts

Cells that reabsorb already existing bones

What is modelling?

Displacement (creates); bone changes, occur along the joints as they increase in size and shape

What is Remodeling?

(Reshapes) growth and changes in existing bone

What is resorption and deposition?

Resorption - Process of removing bone

Deposition - process of laying down or adding new bone

When does remodelling occur?

Response to forces placed on tooth within its socket

• When tooth moves, bone in front will be reabsorbed and be deposited in the space behind and filled with new bone

What is the process of tooth formation called and its 3 primary periods?

Odontogenesis:

1. Growth

2. Calcification

3. Eruption

What are the 3 stages of the growth period?

1. Bud Stage

2. Cap Stage

3. Bell Stage

What happens in the bud stage?

Initiation stage, formation of the tooth begins

What happens in the cap stage?

Proliferation stage, cells of developing tooth increase

Embryonic ectoderm layer matures into enamel

What happens in the bell stage?

Histodifferentiation and morphodifferentiation stage, different tissues of teeth form and its shape are established

Enamel, dentin, cementin, start to form parts of tooth

What are the cells that form enamel, dentin, and cementin called?

Ameloblasts, Odontoblasts, Cementoblasts

When does the initiation stage, bud stage, cap stage, and bell stage begin?

Initiation stage - 6th to 7th week

Bud stage - 8th week

Cap stage - 9th to 10th week

Bell stage - 11th to 12th week

What is calcification

When the structural outline of the tooth is formed

During growth stage, hardened by deposits of calcium or other mineral salts

How does the ameloblast build dentin

Layer by layer going outward starting from dentoenamel junction and the top of the crown

What is a fissure?

Fault along a developmental groove on occlusal surface

Caused by incomplete or imperfect joining of the lobes during formation of tooth

What is a pit?

Two developmental grooves cross each other, formation of a deep area that is too small for tooth brush to clean

What is an eruption?

Movement of tooth into its functional position

True or false: Does the eruption of primary dentition takes place in chronological order, as permanent dentition?

True

What are the natural spaces that occur between primary teeth called?

Primate spaces

What is another name for permanent teeth?

Succedaneous teeth

What is another name for primary teeth?

Deciduous teeth

What is shedding / exfoliation?

Normal process as how primary teeth is lost

How does shedding work?

Osteoclasts reabsorb root of primary teeth starting from the apex then towards the crown

Crown of the tooth gradually lacks support and becomes loose and falls off

What is oral histology?

Study of the structure and function of teeth and oral tissues

Describe the crown

• In the crown dentin is covered by enamel

What is an anatomical crown?

Portion of the tooth that is covered with enamel

What is a clinical crown?

Portion of the tooth visible in the mouth

Name the dental tissues on a tooth diagram

• Maxillary / mandibular alveolar process

• Enamel

• Dentin

• Cementoenamel junction

• Pulp cavity

• Periodontal ligaments

Describe the root

• Partially embedded in the alveolar process

• In the root the dentin is covered with cementum

What is it called when one tooth’s root divides into 2 roots and one where it divides into 3?

Bifurcation - Division into 2 roots

Trifurcation - Division into 3 roots

What the end of a root tip called?

Apex

What is it called something is situated at the apex?

Apical

What is it called when it’s surrounding the apex?

Perioapical

Describe the enamel

• Formed by Ameloblasts

• Hardest material of the tooth body

• Thin

• Yellow to grayish white

• Consists of 96%-99% inorganic matter

• 1%-4% organic matrix

• Composed of millions of calcified enamel prisms called enamel rods

What is Hydroxyapatite?

Inorganic mineral component which consists primarily of calcium

What are enamel rods?

Structural units of enamel

True or False: Enamel is capable of repair

False

Describe dentin

• Makes up main portion of tooth structure

• Extends almost entire length of the tooth

• Covered by enamel on the crown

• Covered by cementum on the root

• Resilient and slightly elastic

• Not as hard as enamel or cementum

What are the 3 major types of dentin?

1. Primary dentin - Born with

2. Secondary dentin

3. Tertiary dentin (reparative dentin)

What is tertiary dentin?

Forms when there is trauma or irritation, self repairing

True or False: Dentin is capable of continued growth and repair

True

Describe cementum

• Bonelike, rigid connective tissue that covers the root

• Joins enamel at the cementoenamel junction

• Anchors tooth to bony socket with attachment fibers within periodontium

When is primary cementum formed?

Forms as the root develops

When does secondary cementum form?

After tooth has reached functional occlusion

Describe the pulp

• Made up of blood vessels and nerves that enter the pulp chamber through the apical foramen

• Blood supply is derived from branches of dental arteries and from periodontal ligaments

True or False: In young teeth the pulp chamber is large and the apical foramen is wide

True

What are the parts in the pulp?

Coronal pulp

Radicular pulp

What happens to the pulp chamber and apical foramen with increasing age?

Secondary dentin decreases the diameter of pulp chamber and apical foramen

Name the parts of dental pulp in a tooth diagram

• Pulp horns

• Coronal pulp

• Accessory canal

• Radicular pulp

• Apical foramen

Describe the periodontium

• Supports the teeth within the alveolar bone

• Consists of cementum, alveolar bone, periodontal ligaments

• Tissues protect and nourish teeth

What are the 2 major units of the periodontium?

Attachment apparatus - Bone, cementum, & periodontal ligaments

Gingival unit - Gums

What is the Lamina dura?

Thin layer of compact bone lining the alveolar socket

What does DEJ stand for?

Dentinoenamel Junction

What does CEJ stand for?

Cementoenamel junction

What is the cortical plate

Dense outer covering of the spongy bone that makes up central part of the alveolar process

What is the alveolar crest?

Highest point of the alveolar ridge

What is the alveolar socket?

Cavity within alveolar process that surround the root of a tooth

What is the difference between interradicular septum and interdental septum?

Interradicular septum - in-between the roots of a tooth

Interdental septum - in-between each tooth

Describe the periodontal ligaments?

• Dense connective tissue organized into fiber groups that connect the cementum with the alveolar bone of the socket wall

• Support tooth in its socket and hold it firmly in normal relationship to surrounding soft and hard tissues

• Acts as the sensory receptors necessary for proper positioning of the jaws during normal functioning

What are periodontal ligaments formed by called?

Fibroblasts