Oral Embryology & Histology

Study Notes

Oral Embryology & Histology

Prenatal development: The study of development before birth, encompassing three stages:
- Pre-implantation Period: First week
- Embryonic Period: Weeks 2-8
- Fetal Period: Weeks 9- birth
Facial development: Occurs during weeks 4-12 of prenatal development.
- Involves all three embryonic layers (ectoderm, mesoderm, endoderm).
- Five processes:
  - Single frontonasal process
  - Paired maxillary processes
  - Paired mandibular processes
Frontonasal process: Develops into the upper face, including:
- Forehead
- Bridge of the nose
- Primary palate
- Nasal septum
- Structures associated with medial nasal processes.
- Placodes: Otic placodes, Nasal placodes, Lens placod
Maxillary process: Formation contributes to the midface, arising from swelling adjacent to the mandibular arch. It gives rise to the:
- Upper lip
- Cheeks
- Secondary palate
- Posterior portion of maxilla
- Maxillary canines and posterior teeth
- Associated tissues
- Zygomatic bones
- Portions of temporal bones.
Primitive mouth (stomodeum): Limited in depth by the oropharyngeal membrane and plays a crucial role in early facial development. The disintegration of the oropharyngeal membrane leads to increased depth of the stomodeum.
Odontoblasts: Form dentin.
Ameloblasts: Form enamel.
Cementoblasts: Form cementum.
Fibroblasts: Form pulp.
Dentin: Highly specialized, calcified connective tissue that is avascular.
- Primary dentin: Formed during tooth development.
- Secondary dentin: Continues to form throughout life.
- Tertiary dentin (Reparative, Reactive): Forms rapidly in response to injury and is localized.
Endoderm: Gives rise to epithelial linings of the respiratory passages, digestive tract, and cells of glandular organs.
Ectoderm: Forms the skin, nervous system, and other structures
Mesoderm: Forms muscles, connective tissues, vessels supplying tissues and organs, and other tissues.
Cementum: Calcified connective tissue:
- Covers the root of teeth.
- Attaches teeth to alveolar bone via periodontal ligament.
- Avascular.
- Continuous formation throughout life.
- Develops from the dental sac.
- Types:
  - Acellular (primary cementum): First layer deposited at the cementodentinal junction.
    - Does not contain cementocytes.
    - Covers the entire root.
    - Does not change in width
  - Cellular (secondary cementum): Last layers deposited over acellular cementum. Deposited mainly at the apical 1/3 of the root.
    - Width changes throughout life
CEJ (Cementoenamel Junction): The junction between the enamel and cementum.
Clinical Crown: The portion of the tooth that is visible in the oral cavity.

Periodontium

Supports teeth in the alveolar bone.
Composed of:
- Gingiva
- Cementum
- Alveolar bone
- Periodontal ligament.

Pulp:

Functions:
- Nutrient delivery
- Formation (new tissue)
- Sensory perception
- Protective function (forms secondary or tertiary dentin)
- Formed from dental papilla.
Involved in:
- Support
- Maintenance
- Continued dentin formation
Consists of connective tissue.
Nerve types:
- Myelinated: Regulate blood flow within vessels.
- Unmyelinated: Responsible for pain perception.
Pulp stones: Calcified masses of dentin that can cause problems during endodontic therapy.
Deposition: The process of laying down or adding tissue.
Resorption: The process of taking away or removing tissue.

Anesthesia & Pain Control

Topical anesthetics: Provide temporary numbing to an area prior to an injection.
- Active ingredients: Benzocaine or lidocaine.
- Forms:
  - Ointment (gel type) - takes approximately 15-30 seconds.
  - Liquid.
  - Spray (for larger surface areas, like gag reflex).
  - Patch (provides anesthesia within 10 seconds, placed on injection site).
Local anesthesia:
- Cartridge information and ingredients:
  - Local anesthetic drug: Depends on the procedure, patient's health, and dentist's preferences.
  - Sodium chloride: Makes the solution isotonic with the body.
  - Vasoconstrictor: Adrenaline is often added to prolong the anesthetic effect and reduce bleeding.
Local anesthetic drugs:
- Lidocaine (Xylocaine)
- Mepivacaine (Carbocaine, Polocaine)
- Prilocaine (Citanest)
- Bupivacaine (Marcaine)
- Articaine (Septocaine)
Anesthetic solutions: Typically contain 2% or 3% local anesthetic with a vasoconstrictor (usually epinephrine).
Dental cartridges: Usually contain 1.8 mL of solution.
Advantages of Local Anesthesia: Pain relief, ease of administration, reversibility, and cost-effectiveness.
Disadvantages of Local Anesthesia: Potential for allergic reactions, side effects, and the need for multiple injections.
Dental injections: Injecting local anesthetic into the tissues surrounding the tooth. The specific injection technique depends on the location and type of procedure.