embryology

Why do dental assistants need to know about dental embryology?

To learn about the DEVELOPMENT OF ORAL STRUCTURES and to understand POSSIBLE DEVELOPMENTAL PROBLEMS IN THE FUTURE

Embryology

The study of prenatal development

Histology

The study of tissue at a microscopic level

When does pregnancy begin?

It begins with conception/fertilization.

After a sperm penetrates the ovum, what happens?

The ovum closes.

How long does pregnancy last?

38-40 weeks

Which trimester is the most crucial for prenatal development?

1st trimester (b/c of embryonic period) b/c cells differentiate and the embryo is the most fragile during this stage.

What are the three periods of prenatal development?

Preimplantation period, embryonic period, fetal phase

When is the preimplantation period?

Week 1

When is the embryonic period?

Week 2 - Week 8

When is the fetal phase?

Week 9 - Week 38-40

Which period is the most critical time for prenatal development?

Embryonic period

When do the face and its related tissues begin to form?

Fourth week (Embryonic period)

What happens to the brain, heart, and stomodeum during the fourth week?

The brain bulges over the oropharyngeal membrane; the heart starts beating; the stomodeum (beginning of mouth) starts to form.

What also happens by the end of the fourth week?

Six pairs of branchial arches have formed

What is the first branchial arch?

The mandibular arch forms the lower lip, the muscles of mastication, and the alveolar process (bone).

What is the second branchial arch?

The hyoid arch is only connected by muscle.

What is the third branchial arch?

It forms the body of the hyoid and the posterior tongue.

What are the three primary embryonic layers?

Ectoderm (outer layer), mesoderm (middle layer), and endoderm (inner layer)

What forms in the ectoderm?

Enamel of teeth

What forms in the mesoderm?

Dentin, pulp, and cementum of teeth

In which primary embryonic layers do teeth form?

The ectoderm and mesoderm layers

What happens during the fifth week?

The embryo is approximately 5 mm long; the heart is prominent and bulging.

What is the only movable bone in head?

The mandible

The palate is formed from which two separate embryonic structures?

The primary and secondary palate (the hard and soft palate are part of the secondary palate)

Any disruption in the development of the palates may result in...

A cleft lip/palate

At 1 month,...

The forehead is the dominant feature

At 4 months,...

The face looks human, the hard and soft palates are beginning to form, and the primary dentition has begun

During the last trimester,...

Fat is laid down in the cheeks (sucking pads)

By the 17th week,...

All primary teeth are developed AND the development of the permanent teeth has begun.

The genetic factors that can cause a disruption in prenatal tooth development are...

Tooth size and jaw size

What are teratogens?

They are adverse environmental influences causing disruption in prenatal tooth development such as infections, drugs, and exposure to radiation.

Osteoclasts

Bone-destroying cells

Osteoblasts

Bone-forming cells

Odontogenesis

The process of tooth formation

What are the three periods of odontogenesis?

Growth, calcification, eruption

What are the three stages of the growth period?

Bud, cap, bell

Bud

Initiation - The formation of the tooth begins

Cap

Proliferation - The cells of the developing tooth increase in number

Bell

Histodifferentiation (different tissues of tooth form) and morphodifferentiation (shape of tooth is established)

Calcification

When the structural outline of the tooth is formed during growth stage and hardened by calcium or other mineral salts. The enamel is built layer by layer working outward

If a tooth has several cusps,...

A cap of enamel forms over each cusp.

Fissure

A fault along a developmental groove caused by incomplete/imperfect joining of the lobes during tooth formation

Pit

When two developmental grooves cross each other, forming a deep area in the tooth.

Eruption

The movement of tooth into the oral cavity in chronological order

Shedding/Exfoliation

The normal process by which the primary teeth are lost

Succedaneous Teeth

Permanent teeth that replace primary teeth

Nonsuccedaneous Teeth

A permanent tooth that does not replace a primary tooth

Crown

Visible part of the tooth; in the crown, dentin is covered by enamel

In the root,...

Dentin is covered by cementum

Anatomical Crown

The portion of tooth that is covered by enamel

Clinical Crown

The portion of the tooth that is visible in the mouth

Root

The portion of tooth embedded in the alveolar process; covered with cementum

Bifurcation

Division into two roots

Trifurcation

Division into three roots

Apex

Tapered end of each root tip

Apical

Anything situated at the apex

Periapical

Anything situated at the surroundings of the apex

Enamel

Hard, outermost layer of a tooth; translucent and appears yellow to grayish-white

Enamel rods

Calcified enamel prisms making up enamel

Dentin

Makes up the main portion of the tooth structure

What are the three major types of dentin?

Primary, secondary, and tertiary

Primary Dentin

Formed before eruption, forms the bulk of the root

Secondary Dentin

Forms after eruption and continues growing at a very slow rate

Tertiary Dentin

Reparative Dentin - Formed in response to irritation and appears as a localized chamber

Cementum

Bonelike, rigid connective tissue covering the root of the tooth; to anchor the tooth to the bony socket with fibers in the periodontium.

Primary Cementum

Formed as the root develops

Secondary Cementum

Formed after the tooth has reached functional occlusion

Pulp

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

Coronal Pulp

The part of the pulp that lies within the crown portion of the tooth

Radicular Pulp

The part of the pulp more apically located

Periodontium

Supports teeth within alveolar bone; consists of cementum, alveolar bone, and periodontal ligaments; divided into attachment apparatus and gingival unit

Alveolar Process

Supports teeth in the jaws

Cortical Plate

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

Alveolar Crest

Highest point of the alveolar ridge

Alveolar Socket

Cavity within the alveolar process that surrounds the root of a tooth

Lamina Dura

The compact bone that lines the alveolar socket

Periodontal Ligament

Dense connective tissue connecting cementum that covers the root of the tooth with the alveolar bone of the stocket wall

Periodontal Ligament Functions

Supportive and Protective: Allows tooth to withstand pressure of mastication Sensory: Nerve fibers in surrounding bone of tooth gives protective "sense of touch" Nutritive: Receive nutrition from blood vessels Formative and Resorptive: Its fibroblasts permit the rapid remodeling for fiber groups

Three Types of Periodontal Ligament Fiber Groups

Periodontal, transseptal, gingival

Periodontal Fiber Group

Supports tooth in socket

Transseptal Fiber Group

Supports tooth inrelation to adjacent teeth

Gingival Fiber Group

Supports gingiva surrounding tooth

Three Main Types of Oral Mucosa

Lining, masticatory, and specialized mucosa

Lining Mucosa

Softer, moist surface, and can stretch and compress (cheeks, vestibule, lips, soft palate, and ventral surface (underside) of tongue

Masticatory Mucosa

Rubbery and resilient/above lining mucosa (attached gingiva, hard palate, and dorsum (upper surface) of tongue)

Specialized Mucosa

Top surface of tongue as papillae (TASTE BUDS)

What are the first primary teeth to erupt?

The two lower central incisors

Each tooth consists of...

A crown and one or more roots